Morphological and structural features of the CdxPb1−xS films obtained by CBD from ethylenediamine-citrate bath Chimica Techno Acta ARTICLE published by Ural Federal University 2021, vol. 8(2), № 20218210 eISSN 2411-1414; chimicatechnoacta.ru DOI: 10.15826/chimtech.2021.8.2.10 1 of 8 Morphological and structural features of the CdxPb1−xS films obtained by CBD from ethylenediamine-citrate bath A.D. Kutyavina a,* , L.N. Maskaeva a,b , V.I. Voronin c , I.А. Anokhina d , V.F. Markov a,b a: Ural Federal University named after the first President of Russia B.N. Yeltsin, 620002, 19 Mira st., Yekaterinburg, Russia b: Ural Institute of the State Fire Service of the EMERCOM of Russia, 620062, 22 Mira st., Yekaterinburg, Russia c: M.N. Miheev Institute of Metal Physics, Ural Branch of Russian Academy of Sciences, 620108, 18 S. Kovalevskaya st., Yekaterinburg, Russia d: Institute of High Temperature Electrochemistry, Ural Branch of the Russian Academy of Sciences, 620990, 20 Akademicheskaya st., Yekaterinburg, Russia * Corresponding author: n-kutyavina@mail.ru This article belongs to the regular issue. © 2021, The Authors. This article is published in open access form under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Abstract The calculating of ionic equilibria in the system «Pb(CH3COO)2  CdCl2  Na3C6H5O7  ‎(NH3)2(CH2)2  N2H4CS» allowed us to find con- ditions and concentration regions of PbS and CdS co-deposition. The determined conditions provided the CBD obtaining of CdxPb1−xS (0 ≤ x ≤ 0.033) substitutional solid solutions films with a cubic structure B1 (space group Fm3̅𝑚) with the grains preferred orientation (200). We established the evolution of the surface morphology of the syn- thesized films from cubic crystallites to hierarchical structure of globular aggregates by scanning electron microscopy. A quantitative analysis of diffraction patterns showed a decrease of microstrains in CdxPb1−xS films by a about factor of 3 with an increase of the cadmi- um chloride concentration in the reaction mixture from 0.005 to 0.14 mol/l. The excess of the cadmium content, established by EDX analy- sis, in the studied films as compared to its content in the solid solu- tion is associated with the additional formation of the amorphous CdS phase up to 72 mol %. Keywords ethylenediamine-citrate bath boundary conditions chemical bath deposition thin films CdxPb1−xS solid solutions Received: 22.03.2021 Revised: 01.06.2021 Accepted: 08.06.2021 Available online: 10.06.2021 1. Introduction Ternary compounds in the CdS-PbS system, f.e. the CdxPb1−xS substitutional solid solutions, have been attract- ing interest among the researchers of semiconductor structures for half a century. The possibility of regulating the band gap from small of PbS (0.4 eV) to rather big of CdS (2.42 eV) value finds application in the production of heterojunctions and solar cells based on these substances [1-2]. The CdxPb1−xS photosensitivity in the range of 0.4- 3.1 μm is used to create IR detectors [3-4]. The developed morphology of the layer surface facilitates using these thin-film compounds as sensitive elements for the deter- mination of toxic compounds in gas and liquid media [5]. Various nanoscale structures are constructed on the basis of CdxPb1−xS solid solutions, in particular, quantum dots, nanocrystals, and nanowires [6-8]. The thin-film CdxPb1−xS solid solutions have the unique functional physical and chemical properties. Semiconduc- tor or ionic conductivity, mechanical, thermal, and radia- tion resistance of these compounds can be controlled by changing the cadmium content or particle sizes making up the film. Also, we can note relative simplicity of their preparation. Many researchers prefer chemical deposition from aqueous solutions (chemical bath deposition, CBD) [1-5,8-20]. This method allows obtaining CdxPb1−xS solid solutions both in powder and thin-film states on sub- strates of any nature and configuration without complex technological equipment. The chemical bath deposition essence of semiconductor compounds is the interaction of metal cations and S 2– ani- ons in solution. The sources of those ions are the metal salt and chalcogenizer, respectively. Ligands allow regu- lating the amount of free metal ions in the reactor due to http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2021.8.2.10 http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0002-1489-1137 Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 2 of 8 the gradual dissociation of complex compounds. Conse- quently, the rate of solid phase formation reduces leading to form a film structure. In situ control the morphology, composition, structure, and semiconducting properties of CdxPb1−xS is possible by varying the components concen- trations in the reaction mixture and the deposition condi- tions (pH of the medium, temperature and duration of synthesis) [9-11], as well as by using different substrates [12]. A typical reaction mixture for the CdxPb1xS solid solu- tions production by CBD includes lead and cadmium salts, mainly Pb(CH3COO)2, Pb(NO3)2 and CdCl2; thiourea (NH2)2CS and various alkaline agents: sodium hydroxide NaOH, aqueous ammonia solution NH4OH, ethylenedia- mine (NH2)2(CH2)2. As for the ligand, different research groups use various substances as complexing agents: triethanolamine (C6H15NO3), aqueous ammonia (NH4OH), ethylenediamine (C2H8N2), sodium citrate (Na3C6H5O7), or a combination thereof. It should be noted that ligands play a key role in the nucleation and growth of a new phase and directly affect the properties of the resulting layers. In a number of works it is quite popular to use either triethanolamine together with an alkaline agent NaOH [13] or an aqueous solution of ammonia [1,17-19], or their combination [10,17,19]. However, the instability of triethanolamine complexes with both lead and cadmium promotes the rap- id transformation of these metal ions into sulfide and the aggregation of sulfide particles in the bulk of the solution. Solid phase precipitates at the reactor bottom in the pow- der form, reducing the thickness of the CdxPb1−xS layer. The use of an ammonia aqueous solution as a complex agent [14] leads to formation of a film surface consisting of spherical particles of ~50 nm. Their shape is further transformed into a plate-like one with increase in the cadmium salt content in the bath. Since ammonia forms stable complexes only with cadmium, in the system under consideration OH – ions act as ligand for Pb 2+ ions. The in- stability constant of the Pb(OH)4 2− tetradentate complex (рk1–4,in = 16.3 [19]) significantly exceeds the values of the Cd(NH3)n 2− complexes instability constants (рk1-4,in = 6.56 [19]). As a result, free cadmium ions prevail in the solu- tion, which leads to the enrichment of the synthesized lay- ers with Cd. Thin-film CdxPb1xS structures (x = 0.35; 0.42; 0.49) synthesized by the authors of [2] had a crystal lattice period of 6.0295–6.0227 Å. That value is more typi- cal of the wurtzite type CdS hexagonal modification (B4, space group P63mc). Attempts to obtain the compositions Cd0.2Pb0.8S and Cd0.4Pb0.6S in [15] and [16] led to the for- mation of CdS films with PbS inclusions. Similar structures consisting of spherical nanoaggre- gates up to 10 nm were obtained from reaction mixtures containing a mixture of triethanolamine and ammonia as ligands [17, 18]. Note that in these publications the au- thors did not give the true composition of the solid solu- tion, indicating only the elemental composition of the compound. However, the thermodynamic assessment of the solid phases PbS and CdS formation [12] showed the possibility of the cadmium cyanamide producing at pH > 10. Impurity phases can negatively affect the properties of the obtained semiconductor layers. To reduce the rate of metal ions release into the solu- tion, Pentia et al. [4] used the disodium salt of ethylenedi- aminetetraacetic acid C10H14N2Na2O8 (EDTA) in an ammo- nia alkaline medium. This ligand provides the strong com- plexes formation of both lead (Pb(EDTA) 2– рk1,in = 18.04 [19]) and cadmium (Cd(EDTA) 2− рk1,in = 16.46 [19]). As a result, films were obtained consisting of a mixture of cubic and tetrahedral crystallites. The films size particles de- creased with an increase in the content of cadmium ions in the reaction bath. Despite the fact that in this work a de- crease the studied CdxPb1−xS films lattice constant was observed, the authors unreasonably assert that the cadmi- um content x in the composition of the solid solution can vary in a wide range from 0 to 1 by fitting of the concen- tration ratio of lead and cadmium salts in a reaction bath. Researchers [3,7,11,12,20] used a reaction mixture con- taining simultaneously two complexing agents: an aque- ous solution of ammonia and sodium citrate. It was found that the CdxPb1−xS solid solutions films deposited from this reaction bath mainly consist of faceted particles whose shape and size depend on the composition [20] and the type of substrate [12]. Nevertheless, in this system there is a possibility of the formation of individual CdS phase [9,12]. The CdS deposition may be associated with the formation of insufficiently stable ammonia complexes of cadmium (the biggest instability constant for the Cd(NH3)4 2− complex рk1-4,in = 6.56 [19]) Hence, the active Cd 2+ ions can arrive intensively into the reaction medium. Ethylenediamine (NH3)2(CH2)2 (En) can be an alterna- tive to aqueous ammonia, because it has weak basic prop- erties for providing an alkaline medium necessary for the hydrolytic thiourea decomposition. Another important advantage of ethylenediamine is its low volatility, which contributes to a constant pH of the reaction mixture. Bear- ing in mind the disadvantage of using the same ligand for lead and cadmium due to their competition, we have de- cided to supplement the formulation by ethylenediamine in addition citrate ions, which are effective for creating stable complexes. Ethylenediamine forms strong complex- es with both lead (Pb(En) 2+ (рk1,in = 7.00); Pb(En)2 2+ (рk1−2,in = 8.45) [21]), and with cadmium (Cd(En) 2+ (рk1,in = 5.63), Cd(En)2 2+ (рk1−2,in = 10.22), Cd(En)3 2+ (рk1−3,in = 12.29) [21]). The ethylenediamine-citrate mixture has proven well in the preparation of CdxPb1−xS solid solutions [9]. Howev- er, the authors of the publication used a rather small range of cadmium salt concentrations (up to 0.025 mol/l). It should be noted that intuitive approaches prevail in the overwhelming majority of publications devoted to the synthesis of CdxPb1−xS solid solutions by CBD. An experi- mental search of the process conditions and of the reac- Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 3 of 8 tion baths compositions is also often encountered accom- panied formal reactions of interaction between precur- sors. Calculation of the concentration range of the lead and cadmium sulfides formation allows predicting the formation of a solid solution before the start of synthesis. Determination of deposition conditions with the least la- bor input is one of the important aims of a researcher us- ing CBD. In this regard, this work is devoted to the ionic equilib- ria analysis with the determination of the potential area of the CdxPb1xS solid solutions formation in the system «Pb(CH3COO)2  CdCl2  Na3C6H5O7  ‎(NH3)2(CH2)2  N2H4CS». The goal of this research is deposition of CdxPb1xS thin films using found formation boundary con- ditions, the study of morphology, composition and crystal structure of these compounds. 2. Experimental The reaction mixture for the chemical bath deposition of CdxPb1−xS solid solutions films included the following components. The precursors were lead acetate Pb(CH3COO)2 0.04 mol/l and cadmium chloride CdCl2. The cadmium salt concentration was varied in the range 0.005–0.14 mol/l. Ethylenediamine ‎(NH3)2(CH2)2 (En) 0.6 mol/l and sodium citrate Na3C6H5O7 (Na3Cit) 0.33 mol/l provided ligands for lead and cadmium ions. Ethylenediamine also served as an alkaline agent, and thi- ourea (NH2)2CS was used as a chalcogenizer. Lead sulfide films were obtained under the same conditions without the cadmium salt in the reaction bath. The films synthesis was carried out on pre-degreased ST-50 sitall substrates in sealed glass reactors (100 ml), which were placed in the TS-TB-10 liquid thermostat heated to 353 K. The process duration was 120 minutes. The thickness of the films was determined using an in- terference microscope (Linnik microinterferometer) MII- 4M with a measurement error of 20%. The microstructure and elemental composition of the films were studied using MIRA 3 LMU scanning electron microscope at the electron beam accelerating voltage of 10 kV and a JEOL JSM-5900 LV scanning electron micro- scope with an EDS Inca Energy 250 energy-dispersive X-ray (EDX) analyzer. X-ray studies of the deposited films were carried out by a PANalytical Empyrean Series 2 diffractometer in Cu Kα radiation in the parallel beam geometry with a position- sensitive PIXel3D detector providing a resolution on 2Θ scale of at least 0.0016°. The diffraction patterns were recorded in 20–100 degrees (2Θ) range with the step of 0.02°, the scanning time was 10 s at a point. The structural parameters of the CdxPb1−xS films were refined by the full-profile Rietveld analysis [22, 23] using the Fullprof software [24]. To separate the contributions of grain size and deformations in the studied films into the width of the diffraction peaks, the conventional William- son – Hall plot equation was used [25]: β∙cosΘ= 0.9λ/D + 4ε∙sinΘ (1) where D is the average size of the coherent scattering re- gions, taken as the average particle size, β is the half- width of the peak in radians, λ is the wavelength of the X- ray radiation used, ε = Δd/d is the deformation, d is the interplanar distance. 3. Thermodynamic assessment of the formation boundary conditions of PbS, CdS, Cd(OH)2 and Pb(OH)2 To determine the CBD optimal conditions, analysis of ionic equilibria was carried out in the system «Pb(CH3COO)2  CdCl2  Na3C6H5O7  ‎(NH3)2(CH2)2 N2H4CS» according to the method proposed in [26]. These calculations allowed estimating the formation regions of the main phases (PbS and CdS) and impurities (Cd(OH)2, Pb(OH)2). The prerequisite for obtaining thin-film metal sulfide is to slow down the rate of the metal salt transformation into sulfide. The rate decreasing is achieved by reducing its active concentration due to the metal ions binding into complex compounds. In the studied system lead ions form complexes with citrate ions Pb(Cit) − (instability constant, рk1,in = 4.34), Pb(Cit)2 4− (рk1−2,in = 6.08), Pb(Cit)3 7− (рk1−3,in = 6.97) [19], Pb(OH)(Cit) 2− (рk1,in = 13.72) [21]; with hy- droxide ions Pb(OH) + (рk1,in = 7.52), Pb(OH)2 (рk1−2,in = 10.54), Pb(OH)3 − (рk1−3,in = 13.95), Pb(OH)4 2− (рk1−4,in = 16.3) [19], and also with ethylenediamine Pb(En) 2+ (рk1,in = 7.00); Pb(En)2 2+ (рk1−2,in = 8.45) [21]. For cadmium, the ligands were ethylenediamine Cd(En) 2+ (рk1,in = 5.63), Cd(En)2 2+ (рk1−2,in = 10.22), Cd(En)3 2+ (рk1−3,in = 12.29) [19], citrate ions Cd(Cit) − (рk1,in = 5.36) [19], Cd(OH)(Cit) 2− (рk1,in = 9.3) [21] and hydroxide ions Cd(OH) + (рk1,in = 3.92), Cd(OH)2 (рk1−2,in = 7.65), Cd(OH)3 − (рk1−3,in = 8.70), Cd(OH)4 2− (рk1−4,in = 8.65) [19]. The regions of individual lead and cadmium sulfides formation, as well as their co-deposition region, were found as a graphical solution of the equilibrium conditions equation in the coordinates “the of the initial metal salt concentration power pCin – the ligand concentration [Na3Cit(En)] – pH” at 298 K [26]: p𝐶in = pSPMS – pαM2+ − (p𝑘H2S 1,2 + 1 2 p𝐾SS − 2pH + 1 2 p[CS(NH2 )2]in + 1 2 p 𝛽c 𝛽s ) − 0.86 ∙ 𝜎 ∙ 𝑉𝑀 𝑅 ∙ 𝑇 ∙ 𝑟𝑐𝑟 , (2) p𝐶in = SPM(OH)2 – pαM2+ – 2p𝐾w + 2pH, (3) where р is the power (negative logarithm); 𝐶in is the lead or cadmium salt initial concentration; pSPMS, pSPM(OH)2 are the solubility products’ powers of sulfides CdS (pSPCdS = 26.6) and PbS (pSPPbS = 27.8) and hydroxides Cd(OH)2 (pSPCd(OH)2 = 15.8) and Pb(OH)2 (pSPPb(OH)2 = 13.66) [19], respectively; [CS(NH2)2]in is the thiocarbamide initial con- centration in solution, equal to 0.6 mol/l; σ is the specific Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 4 of 8 surface energy of metal sulfide (σPbS = 1.2 J/m 2 and σСdS = 0.9 J/m 2 ); Vm is the molar volume of the synthesized phase Vm(PbS) = 31.9∙10 -6 m 3 /mol and Vm(CdS) = 29.97∙10 -6 m 3 /mol; rcr is the critical nucleus radius (3.5∙10 −9 m) [26]; R is the ideal gas constant, J/(mol∙K); Т is the temperature of the process, 298 K; p𝑘H2S 1,2 is the hydrogen sulfide dissociation constant, 1.3∙10 20 [19]; 𝐾SS is the thiourea hydrolytic de- composition constant, 3.2∙10 23 [27]; βs and βc are the val- ues that include the dissociation constants of hydrogen sulfide H2S and cyanamide H2CN2, calculated by the ex- pressions 𝛽s = [H3 O + ]2 + 𝑘HS− 1 [H3O +] + 𝑘H2S 1,2 , 𝛽c = [H3 O +]2 + 𝑘HCN2− 1 [H3O +] + 𝑘H2CN2 1,2 , where 𝑘HS− 1 , 𝑘HCN2− 1 and 𝑘H2S 1,2 , 𝑘H2CN2 1,2 are the first stage dissociation constants of hydrogen sul- fide and cyanamide (𝑘HS− 1 = 6.99 [19], 𝑘HCN2− 1 = 10.33 [27]) and their cumulative ones (𝑘H2S 1,2 = 19.59 [19], 𝑘H2CN2 1,2 = 21.51 [27]); pαM2+ is the power of the fraction of free lead or cadmium ions in uncomplexed forms. The calculation was carried out considering all possible lead and cadmium forms according to the method proposed in [26]. The last term in Eq. (2) is the derivative of the Thomson - Ostwald relation. This expression determines the supersaturation contribution of lead or cadmium sulfide in the system, taking into account the formation of critical size nuclei. Sulfide ions formed during the decomposition of thiou- rea are distributed between the ions of two metals. Hence the CdxPb1xS solid solution formation will occur by way of competing reactions of the CdS and PbS formation. To ex- clude the limiting effect of the chalcogenizer, the deposi- tion of CdxPb1xS solid solutions was carried out with an excess of thiourea concentration by about 3–13 times com- pared with the metal concentrations in the reaction mix- ture. Thermodynamic assessment of potential regions of the sparingly soluble phases formation in the studying system was performed at a temperature of 298 K under varying the concentration of ethylenediamine (En) from 0.1 to 1.0 mol/l (a) and sodium citrate (Na3Cit) from 0.1 to 0.6 mol/l (b) considering the crystallization factor (Fig. 1). The pre- dicted simultaneous deposition area of CdS and PbS solid phases corresponds to the space lying between the surfac- es characterizing the initial conditions for the deposition of sulfides (upper surfaces) and hydroxides (lower surfac- es) of these metals. In three-dimensional coordinates pCin = f(pH, [L]) the plotted dependences reveal that the CdPbS ternary compound formation without hydroxides admix- tures begins with the cadmium sulfide precipitation at pH = 10–14 (a) and 10–12 (b). In the less alkaline region (pH = 8-10) the process begins with the PbS formation. The simultaneous deposition area of solid phases of both PbS, CdS sulfides and hydroxides Pb(OH)2 and Cd(OH)2 is situated under the concentration planes of the lead and cadmium hydroxides (lower surfaces) formation at pH 11.7–14.0 (a) and 11.2–14.0 (b). It should be noted that, in the system under discussion, the sulfides for- mation occurs according to a heterogeneous mechanism by sulfidization of lead and cadmium hydroxides at pH > 11. The reaction mixture composition was formed from calculations and preliminary experiments. Mirror films with good adhesion to the substrate were obtained with varying the concentration of cadmium salt (0.005–0.14 mol/l). The synthesized films were 400 to 650 nm thick. A change in the gray color (characteristic of PbS) to a dark blue and light green hue (imparted by the content cadmi- um) indicated the CdPbS three-component compound for- mation. 4. Results and Discussion The morphology of PbS films (a) and CdPbS thin-film ter- nary compounds obtained from reaction baths containing 0.01 (b) and 0.1 mol/l (c) CdCl2 is shown in Fig. 2. Fig. 1 Boundary conditions of the PbS, CdS, Pb(OH)2 and Cd(OH)2 sparingly soluble phases formation depending on the pH of the medi- um and the concentration of ethylenediamine (En) (a) and sodium citrate Na3Cit (b). Calculations were performed at [Na3Cit] = 0.3 mol/l (a) and [En] = 0.6 mol/l (b), Т = 298 K a b Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 5 of 8 Fig. 2 SEM images of PbS (a) and CdPbS films obtained from reaction baths containing (b) 0.01 and (c) 0.1 mol/l CdCl2 The lead sulfide film analysis revealed that the average observed crystallite size was ~150–200 nm, and the film continuity degree did not exceed ~80% (Fig. 2a). The min- imum cadmium salt amount introduction (0.01 mol/l) into reactor led to a slowdown in the rate of formation of lead sulfide, which was also noted by the authors in [28], and the formation of a uniform film consisting of cubic crystal- lites with an edge of ~150 nm. The particles did not com- pletely cover the substrate surface (Fig. 2b). The cubic grains shape is due to the presence in the system of suffi- ciently stable ethylenediamine complexes of lead. The de- struction of these complexes requires additional energy, which increases the energy barrier of interaction between lead and thiourea ions. According to [29], the process pro- ceeds in a thermodynamic regime, the crystallites grows along the <111> directions. The radical change in the CdPbS films morphology has occurred with the 0.1 mol/l cadmium chloride introduction into the reaction mixture. The obtained films grains com- posed of the spherical globules ~300–400 nm in size, rep- resenting clusters of nanoparticles 50–70 nm in size (Fig. 2c). The presence of the hierarchical structure char- acteristic of CdS [30] is a consequence of the block deposi- tion mechanism implementation. In the bulk of the reac- tion mixture, solid phase clusters form followed by deposi- tion on the substrate surface [31]. The crystal structure of solid solution films deposited from solutions with 0.005, 0.01, 0.1, 0.12, and 0.14 mol/l concentrations of cadmium chloride was studied by X-ray diffraction. XRD patterns of the synthesized PbS and ter- nary CdPbS compounds are shown in Fig. 3. The observed peaks corresponded to the PbS cubic structure B1 (space group Fm3̅m) and to the sitall substrate (TiO2 and cordier- ite). The gradual shift of all reflections to the region of greater angles 2Θ evidences solid solutions formation (Fig. 3, inset). As a result, a slight decrease of the period cubic lattice B1 is observed from 0.5933(8) to 0.5929(2), 0.5923(6), 0.5918(0), 0.5920(7), and 0.5918(0) nm (Ta- ble 1). Fig.3 X-ray diffraction patterns of PbS film and CdxPb1−xS solid solution films obtained at different CdCl2 contents in the reaction bath. The inset shows the (311) B1 peak shift of the CdxPb1−xS films to 2Θ high-angle region. a b c Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 6 of 8 The observed crystal lattice period decrease is due to the replacement of lead (II) ions (r = 0.120 nm [32]) by cadmium ions with smaller radius (r = 0.097 nm [32]) in the PbS structure. To estimate the relative content of cad- mium and lead, we used the CdxPb1−xS (aSS) solid solutions lattice period decreasing (aSS), the experimental value for PbS aPbS = 0.5933(8) nm, and the lattice period for the pseudocubic В1 structure aCdS=0.546 nm given in [33–36]. Vegard's rule was used [37-38] to determine the (х) cad- mium relative content in CdxPb1−xS solid solutions. Accord- ing to Vegard's rule, the molar fraction of cadmium is de- fined as x = (aPbS –aSS)/(aPbS− aCdS). The performed calculation allowed us to establish the relative content of cadmium x in the lead metal sublattice with an accuracy of ± 0.001 (Table 1). Comparison of the established solid solutions compositions (Table 1) with the PbS - CdS system equilibrium phase diagram [39] indi- cates a significant supersaturation of the lead sulfide lat- tice by cadmium for all synthesized CdxPb1−xS solid solu- tions (0 , sizes of coherent scattering regions D given for CdxPb1xS thin films obtained with different concentrations of [CdCl2] cadmium chloride in the reaction bath. Content of the cadmium salt in the reaction bath, [CdCl2], mol/l 0 0.005 0.01 0.1 0.12 0.14 аВ1 (nm) 0.00001 0.5933(8) 0.5933(1) 0.5929(2) 0.5923(6) 0.5920(7) 0.5918(0) x in CdxPb1xS − 0.001 0.010 0.022 0.028 0.033 T200 (%) T111 (%) − 35.6 22.5 − 24.2 − 24.5 − 21.8 − 28.2 − <d/d>, ∙10 4 4.8 11.5 6.0 6.2 5.7 3.5 D, nm 110 138 123 139 130 77 Table 2 Effect of the concentration of cadmium chloride on the composition of СdxPb1-xS solid solutions. Composition of the reaction mixture, mol/l: [PbAc2] = 0.4, [En] = 0.6, [TM] = 0.6, [Na3Cit] = 0.3. The temperature of synthesis was 353 K. [CdCl2], mol/l Content of elements in the film, at % Formula composition of the film (without separation into crystalline and amorphous phases) Formula composition of the CdхPb1−хS solid solution, estimation by the lattice parameter, ±0.004 Phase composition of the film, mol % Cd ±0.07 Pb ±0.05 S ±0.08 CdхPb1−хS solid solution СdS amor- phous sulfide 0.005 9.54 40.45 50.01 Cd0.19Pb0.81S0.99 Cd0.001Pb0.999S ~81 19 0.01 16.35 34.09 49.56 Cd0.32Pb0.68S1.02 Cd0.010Pb0.990S 69 31 0.10 34.14 16.77 49.09 Cd0.67Pb0.33S1.04 Cd0.022Pb0.978S 34 66 0.12 36,79 13,84 49,36 Cd0.73Pb0.27S1.03 Cd0.028Pb0.972S 28 72 0.14 37.39 13.87 48.74 Cd0.73Pb0.27S1.05 Cd0.033Pb0.967S 28 72 Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 7 of 8 films contain, in addition to 28–81 mol.% crystalline СdxPb1−xS, 19–72 mol.% the cadmium sulfide amorphous phase. The high content of the CdS amorphous phase in the synthesized films was due to the more favorable condi- tions for CdS formation at the pH of thiourea hydrolytic decomposition (pH = 11-12). That assumption is consistent with the potential thermodynamic area assessment of CdS and PbS sulfides co-precipitation in the system under dis- cussion. 5. Conclusions The concentration regions of the isovalent lead sulfides PbS and cadmium CdS co-precipitation were determined based on the ionic equilibria analysis in the system «Pb(CH3COO)2  CdCl2  Na3C6H5O7  ‎(NH3)2(CH2)2  N2H4CS». For the studied system, these calculations al- lowed defining the deposition parameters of the CdxPb1xS substitutional solid solutions. Films of supersaturated CdxPb1xS solid solutions with the cadmium content up to x = 0.033 were obtained by chemical bath deposition at 353 K on sitall substrates. The crystalline structure of the films was B1 cubic (space group Fm3̅m). SEM analysis of CdPbS films demonstrated the evolu- tion of the morphology layers. The polycrystalline struc- ture has replaced by globular aggregates with increasing of the cadmium chloride concentration up to 0.14 mol/l in the reaction bath. The higher cadmium content in the CdPbS films found by EDX analysis in comparison with its amount estimated from the XRD data is associated with the formation of the CdS amorphous phase. Acknowledgements The research was financially supported by 211 Program of the Government of the Russian Federation (No. 02.A03.21.0006), was carried out within the state assignment of Ministry of Science and Higher Education of the Russian Federation (theme No. Н687.42Б.223/20) and supported by RFBR (projects No. 20-48-660041). References 1. Suryavanshi KE, Dhake RB, Patil AM, Sonawane MR. Growth mechanism and transport properties of chemically deposited Pb Cd S thin film’s photoelectrochemical (PEC) solar cell. Optik. 2020;165008. doi:10.1016/j.ijleo.2020.165008 2. Ounissi A, Ouddai N, Achour S. Optical characterisation of chemically deposited Pb(1−x)CdxS films and a Pb1−xCdxS(n)/Si(p) heterojunction. Eur Phys J Appl Phys. 2007;37(3):241−5. doi:10.1051/epjap:2007034 3. Maskaeva LN, Markov VF, Porkhachev MYu, Mokrousova АО. Thermal and radiation stability IR-detectors based on films of solid solutions CdxPb1−xS. Pozharovzryvobezopasnost [Fire and Explosion Safety]. 2015;24(9):67-73. Russian. doi:10.18322/PVB.2015.24.09.67-73 4. Pentia E, Draghici V, Sarau G, et al. Structural, electrical, and photoelectrical properties of CdxPb1−xS  thin films prepared by chemical bath deposition. J Electrochem Soc. 2004;151(11):G729−33. doi:10.1149/1.1800673 5. Bezdetnova AE, Markov VF, Maskaeva LN, et al. Determina- tion of nitrogen dioxide by thin-film chemical sensors based on CdxPb1–xS. J Anal Chem. 2019;74(12):1256−62. doi:10.1134/S1061934819120025 6. Au GHT, Shih WY, Tseng SJ, Shih WH. Aqueous CdPbS quantum dots for near-infrared imaging. Nanotechnology. 2012;23(27):275601(1-9). doi:10.1088/0957-4484/23/27/275601 7. Tan GL, Liu L, Wu W. Mid-IR band gap engineering of CdxPb1−xS nanocrystals by mechanochemical reaction. AIP Advances. 2014;4(6):067107(1-11). doi:10.1063/1.4881878 8. Nichols PL, Liu Z, Yin L, et al. CdxPb1–xS alloy nanowires and heterostructures with simultaneous emission in mid-infrared and visible wavelengths. Nano Lett. 2015;15(2):909−16. doi:10.1021/nl503640x 9. Rabinovich E, Wachtel E, Hodes G. Chemical bath deposition of single-phase (Pb,Cd)S solid solutions. Thin Solid Films. 2008;517(2):737−44. doi:10.1016/j.tsf.2008.08.162 10. Barote M, Yadav A, Masumdar E. Effect of deposition parame- ters on growth and characterization of chemically deposited Cd1-xPbxS thin films. Chalcogenide Lett. [Internet]. 2021[cited 2021];8(2):129−38. Available from: https://chalcogen.ro/index.php/journals/chalcogenide- letters/11-cl/126-volume-8-number-2-february-2011 11. Maskaeva, LN, Kutyavina AD, Markov VF, et al. Features of the formation of thin films of supersaturated CdxPb1–xS solid solutions by chemical bath deposition. Russ J Gen Chem. 2018;88(2):295–304. doi:10.1134/S1070363218020172 12. Maskaeva LN, Pozdin AV, Markov VF, et al. Effect of the sub- strate nature on the CdPbS film composition and mechanical stresses at the “film–substrate” interface. Semiconductors. 2020;54:1567–76. doi:10.1134/S1063782620120209 13. Rajathi S, Kirubavathi K, Selvaraju K. Preparation of nano- crystalline Cd-doped PbS thin films and their structural and optical properties. J of Taibah University for Science. 2017;11(6):1296−305. doi:10.1016/j.jtusci.2017.05.001 14. Suryavanshi KE, Dhake RB, Patil AM, Sonawane MR. Growth mechanism and transport properties of chemically deposited PbCdS thin film’s photoelectrochemical (PEC) solar cell. Optik. 2020;165008. doi:10.1016/j.ijleo.2020.165008 15. Ahmad SM, Kasim SJ, Latif LA. Effects of thermal annealing on structural and optical properties of nanocrystalline CdxPb1-xS thin films prepared by CBD. Jordan Journal of Physics [Internet]. 2016[cited 2021];9(2):113−22. Available from: http://journals.yu.edu.jo/jjp/JJPIssues/Vol9No2pdf2016/7.pd f 16. Suryavanshi KE, Dhake RB, Patil AM, et al. Structural proper- ties of PbxCd1−xS thin films prepared by chemical bath deposi- tion technique. Int J Adv Res [Internet]. 2014[cited 2021];2(6):491−3. Available from: http://www.journalijar.com/uploads/926_IJAR-3389.pdf 17. Thangavel S, Ganesan S, Chandramohan S, et al. Band gap engineering in PbS nanostructured thin films from near-infrared down to visible range by in situ Cd-doping. J Alloys Comp. 2010;495(1):234237. doi:10.1016/j.jallcom.2010.01.135 18. Deo SR, Singh AK, Deshmukh L, et al. Studies on structural, morphological and optical behavior of chemically deposited Cd0.5Pb0.5S thin films. Optik. 2015;126(20):2311–17. doi:10.1016/j.ijleo.2015.05.130 19. Lurie YuYu. Spravochnik po analiticheskoy khimii [Analytical chemistry handbook]. Мoscow: Khimiya; 1989. 488 p. Russian. https://doi.org/10.1016/j.ijleo.2020.165008 https://doi.org/10.1051/epjap:2007034 https://doi.org/10.18322/PVB.2015.24.09.67-73 https://doi.org/10.1149/1.1800673 https://doi.org/10.1134/S1061934819120025 https://doi.org/10.1088/0957-4484/23/27/275601 https://doi.org/10.1063/1.4881878 https://doi.org/10.1021/nl503640x https://doi.org/10.1016/j.tsf.2008.08.162 https://chalcogen.ro/index.php/journals/chalcogenide-letters/11-cl/126-volume-8-number-2-february-2011 https://chalcogen.ro/index.php/journals/chalcogenide-letters/11-cl/126-volume-8-number-2-february-2011 https://doi.org/10.1134/S1070363218020172 https://doi.org/10.1134/S1063782620120209 https://doi.org/10.1016/j.jtusci.2017.05.001 https://doi.org/10.1016/j.ijleo.2020.165008  http://journals.yu.edu.jo/jjp/JJPIssues/Vol9No2pdf2016/7.pdf http://journals.yu.edu.jo/jjp/JJPIssues/Vol9No2pdf2016/7.pdf http://www.journalijar.com/uploads/926_IJAR-3389.pdf https://doi.org/10.1016/j.jallcom.2010.01.135 https://doi.org/10.1016/j.ijleo.2015.05.130 Chimica Techno Acta 2021, vol. 8(2), № 20218210 ARTICLE 8 of 8 20. Maskaeva LN, Voronin BI, Mostovshchikova EV, et al. Chemical bath deposited CdxPb1-xS solid solution films: com- position, structure, optical properties. Thin Solid Films. 2021;718(12):138468. doi:10.1016/j.tsf.2020.138468 21. Nikolsky BP. Spravochnik khimika. Tom 3 [Chemist's hand- book. Volume 3]. Leningrad: Khimiya; 1971. 1008 p. Russian. 22. Rietveld HM. A profile refinement method for nuclear and magnetic structures. J Appl Crystallogr. 1969;2(2):65−71. doi:10.1107/S0021889869006558 23. Bush DL, Post JE. A survey of using programs for the Rietveld profile refinement. Reviews in mineralogy. 1990;20:369−74. doi:10.1180/claymin.1990.025.4.12 24. Rodriges-Carvajal J. Recent advances in magnetic structure determination by neutron powder diffraction. Physica B. 1993;192:55−69. doi:10.1016/0921-4526(93)90108-I 25. Williamson GK, Hall WH. X-ray line broadening from filed aluminium and wolfram. Acta Metall. 1953;1:22−31. doi:10.1016/0001-6160(53)90006-6 26. Maskaeva LN, Markov VF, Vaganova IV, et al. Films of super- saturated CdxPb1−xS solid solutions: composition prognostica- tion, chemical synthesis, microstructure. Russ J Appl Chem. 2017;90(5):691–700. doi:10.1134/S1070427217050044 27. Vinogradova TV, Markov VF, Maskaeva LN. Temperature dependence of constants of thiourea hydrolytic decomposi- tion and cyanamide. Stepwise ionization. Russ J Gen Chem. 2010;80:2341–6. doi:10.1134/S1070363210110198 28. Maskaeva LN, Markov VF, Forostyanaya NA, et al. Kinetic aspects of hydrochemical deposition of cadmium sulfide from solutions with diverse ligand backgrounds. Russ J Gen Chem. 2016;86(10):2273−81. doi:10.1134/S1070363216100054 29. Lee S-M, Cho S-N, Cheon J. Anisotropic shape control of col- loidal inorganic nanocrystals. Adv Mater. 2003;15(5):441−4. doi:10.1002/adma.200390102 30. Forostyanaya NA, Maskaeva LN, Markov VF. Influence of the ligand nature on the boundary conditions of the formation and the morphology of nanocrystalline cadmium sulfide films. Russ J Gen Chem. 2015;85:2513–19. doi:10.1134/S1070363215110031 31. Markov VF, Maskaeva LN. Nucleation and mechanism of metal sulfide film growth using deposition by thiocarbamide. Russ Chem Bull. 2014;63(7):1523−32. doi:10.1007/s11172-014-0630-7 32. Bugaenko LT, Ryabykh SM, Bugaenko AL. A nearly complete system of average crystallographic ionic radii and its use for determining ionization potentials. Moscow Univ Chem Bull. 2008;63:303–17. doi:10.3103/S0027131408060011 33. Kobayashi T, Susa K, Taniguchi S. Preparation and semicon- ductive properties of rock salt type solid solution systems, Cd1−xMxS (M = Sr, Ca, Mg, Pb, Sn). J Phys Chem Solids. 1979;40:781−5. doi:10.1016/0022-3697(79)90160-4 34. Corll JA. Recovery of the high‐pressure phase of cadmium sulfide. J Appl Phys. 1964;35(10):3032–3. doi:10.1063/1.1713151 35. Rooymans CJM. Structure of the high pressure phase of CdS, CdSe, and InSb. Phys Lett. 1963;4:186−7. doi:10.1016/0031-9163(63)90356-1 36. Susa K, Kobayashi T, Taniguchi S. High-pressure synthesis of rock-salt type CdS using metal sulfide additives. J Solid State Chem. 1980;33:197−202. doi:10.1016/0022-4596(80)90120-6 37. Vegard L. Die konstitution der mischkristalle und die raumfüllung der atome. Zeitschrift für Physik. 1921;5:17−26. doi:10.1007/BF01349680 38. Denton AR, Ashcroft NW. Vegard’s law. Phys Rev A. 1991;43:3161−4. doi:10.1103/PhysRevA.43.3161 39. Shelimova LE, Tomashik VN, Gritsyv VI. Diagrammy sos- toyaniya v poluprovodnikovom materialakh (sistemy na os- nove khal'kogenidov Si, Ge, Sn, Pb) [State diagrams in semi- conductor materials science (systems based on chalcogenides Si, Ge, Sn, Pb]. Moscow: Nauka; 1991. 368 p. Russian. https://doi.org/10.1016/j.tsf.2020.138468 https://doi.org/10.1107/S0021889869006558 https://doi.org/10.1180/claymin.1990.025.4.12 https://doi.org/10.1016/0921-4526(93)90108-I https://doi.org/10.1016/0001-6160(53)90006-6 https://doi.org/10.1134/S1070427217050044 https://doi.org/10.1134/S1070363210110198 https://doi.org/10.1134/S1070363216100054 https://doi.org/10.1002/adma.200390102 https://doi.org/10.1134/S1070363215110031 https://doi.org/10.1007/s11172-014-0630-7 https://doi.org/10.3103/S0027131408060011 https://doi.org/10.1016/0022-3697(79)90160-4 https://doi.org/10.1063/1.1713151 https://doi.org/10.1016/0031-9163(63)90356-1 https://doi.org/10.1016/0022-4596(80)90120-6 https://doi.org/10.1007/BF01349680 https://doi.org/10.1103/PhysRevA.43.3161