The effect of processing conditions on the dielectric properties of doped calcium lanthanum nickelate


 
published by Ural Federal University 

eISSN 2411-1414; chimicatechnoacta.ru 
ARTICLE 

2022, vol. 9(4), No. 20229410 

DOI: 10.15826/chimtech.2022.9.4.10 
 

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The effect of processing conditions on the dielectric properties 
of doped calcium lanthanum nickelate  

Yulia A. Deeva a* , Abdullo A. Mirzorakhimov a , Alexey Yu. Suntsov b , 
Nadezhda I. Kadyrova b , Nina V. Melnikova a, Tatyana I. Chupakhina b   

a: Institute of New materials and technologies, Ural Federal University, Ekaterinburg 620009, Russia  
b: Institute of Solid State Chemistry UB RAS, Ekaterinburg 620990, Russia 

* Corresponding author: juliahik@mail.ru 

This paper belongs to a Regular Issue. 

© 2022, the Authors. This article is published in open access under the terms and conditions of the Creative  

Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). 

 

  

Abstract 

The influence of thermal and thermobaric (TBT) effects on the struc-

ture, microstructure, and dielectric properties of ceramics based on 

solid solutions of the La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) composition 

was studied. TBT treatment of the samples leads to a change in the 

grain morphology of ceramics and an increase in the dielectric con-

stant compared to its value only after heat treatment. The change in 

the anisotropy of the coordination (La,Ca)O9 and (Ni,M)O6 polyhedra 

after TBT contributed to interlayer polarization in the crystal struc-

ture of La1.8Ca0.2Ni0.8M0.2O4+δ. 

Keywords 
ceramics  

solution combustion 

thermobaric treatment 

impedance spectroscopy 

dielectric response 

Received: 22.07.22 

Revised: 10.08.22 

Accepted: 11.08.22 

Available online: 23.08.22 

1. Introduction 

The search for materials with a high dielectric constant and 

low dielectric losses is one of the main tasks of modern ma-

terials science. However, this problem does not have a simple 

solution since an increase in the dielectric constant (ε) is ac-

companied by an increase in dielectric losses (tan δ) and the 

dependence of dielectric parameters on temperature. 

For the first time, a very high value of the permittivity 

was found in single crystals of layered perovskite-like oxides, 

such as CaCu3Ti4O12, La15/8Sr1/8NiO4 (structural type K2NiF4, 

for oxides – A2BO4) and solid solutions based on them; the 

value was ε is very large [1, 2]. In the lanthanum-strontium 

nickelate, this characteristic is frequency- and temperature 

independent, which makes this material promising for prac-

tical applications (ε ~ 105–106) [3, 4]. In ceramic samples and 

thin films of CaCu3Ti4O12 and La15/8Sr1/8NiO4, the dielectric 

constant has a lower value and decreases with an increase in 

the frequency of the electric field [3, 5]. It was found that the 

ceramics obtained by the thermobaric method have better di-

electric characteristics in comparison with those of the sam-

ples obtained by the ceramic technology at atmospheric pres-

sure [6, 7]. At a low frequency (102 Hz), the dielectric con-

stant and dielectric losses of CaCu3Ti4O12 (CCTO) increase 

with an increase in the calcination temperature and an in-

crease in the grain size [8]. Thus, CCTO had the highest die-

lectric constant and tan δ values. At the middle frequency 

(103–105 Hz), CCTO was found to exhibit the lowest tan δ 

value (0.091). 

Among ceramics based on complex oxides with a struc-

ture of the type K2NiF4 (for oxides, the formula is written 

as А2ВО4), which have been extensively researched over the 

past decade, the compounds with both temperature- and 

frequency-independent giant dielectric constant 

(Ln2−xSrxNi1−yMyO4 (Ln – rare earth element (REE), M = Co, 

Cu; ε ~ 103–106, tan δ>1.0), and with a low tangent of the 

dielectric loss angle (А2−xLnxTi1−yMyO4 (A = Ca, Sr); ε ~ 10–

30, tan δ<10−3) were found [9]. 

It is known that a high dielectric constant in REE-

strontium layered nickelates is realized due to interlayer 

charge polarization, which is influenced by structural ani-

sotropy. Structural distortions of the AO9 and BO6 coordi-

nation polyhedra can be regulated by partial or complete 

substitution of cations in the position A. The dielectric re-

sponse suddenly changes with changing the rare earth ion, 

when the crystal symmetry changes, so there should be a 

link between the dielectric response and crystal symmetry 

[6, 10]. Of the unsubstituted nickelates, the Sm1.5Sr0.5NiO4 

compound has the best characteristics (ε = 106, tan δ<0.1), 

but these parameters are unstable and depend on the tem-

perature and frequency of the electric field [11]. It should 

be noted that the difference between the radii of Sm and Sr 

(coordination number of which is IX) leads to the formation 

of an oxide with orthorhombic symmetry [12], in contrast 

with the analogous compounds, La-, Pr-, Nd-containing 

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Chimica Techno Acta 2022, vol. 9(4), No. 20229410 ARTICLE  

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ones, crystallizing in the tetragonal modification [13–15]. In 

solid solutions (Sm1−xNdx)1.5Sr0.5NiO4 the orthorhombic 

phase exists for x<0.6, while for 0.6<x<1.4 the structure 

becomes tetragonal [16], and after this transition ε falls and 

tan δ increases. 

The relationship between dielectric characteristics and 

structural anisotropy due to the replacement of La 

(r = 1.31 Å) by Ca cation (r = 1.01 Å) was described in [17] 

using the La2−xCaxNiO4 solid solution as an example. It was 

shown that the distortions of the AO9 and BO6 polyhedra 

change at different x, which allowed the authors to obtain 

a compound with a high ε ~ 104 (x = 0.2), but a rather high 

value of tan δ ~ 100 (x = 0.3). In the resulting oxides, the 

dielectric constant strongly depends on frequency and tem-

perature, which is unusual for compounds of this class. 

There are no other data on the dielectric properties of Ca-

substituted nickelates of lanthanum and other rare-earth 

elements in the literature. 

On the other hand, the parameters of the А2ВО4 struc-

ture change upon partial substitution of elements located 

not only in the A position, but also in the B position, espe-

cially if the substitution is heterovalent. In this case, the 

interlayer polarization is affected not only by structural dis-

tortions, but also by the charge state of the cations that 

make up the oxide [18]. 

Investigation of the dielectric characteristics of 

(La,Ca)(Ni,M)O4 (M = Cu, Co) ceramics, the results of 

which we present in this work, was aimed at studying the 

nature of high dielectric permittivity in layered perovskite-

type oxides with a K2NiF4 type structure.  

The choice of Co and Cu as substitute elements is due to 

the Jahn-Teller nature of the Cu2+ cation and the preferred 

oxidation state of Co3+ at high temperatures, which should 

have a significant effect on the structural anisotropy. Elon-

gations of BO6 octahedra along the c axis in the presence of 

Cu2+ in position B, as shown in [19], stabilizes the fre-

quency-independent behavior of the dielectric constant in 

lanthanum-strontium nickelates, and the presence of Co3+ 

increases the dielectric constant [6].  

Another, no less important task of this study was to in-

vestigate the influence of the sample morphology on the di-

electric characteristics.  

Thermobaric treatment changes the microstructure of 

the samples, which has a noticeable effect on the dielectric 

properties of ceramics based on oxide compounds. Strong 

influence on the dielectric parameters is exerted by the 

Maxwell-Wagner polarization at grain boundaries and in-

homogeneities. This effect refers to external factors that af-

fect the dielectrics parameters value. 

In this paper, ceramic samples of K2NiF4 structural type, 

which have a composition La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, 

Cu) were investigated. To improve the dielectric properties 

of ceramics based on the complex oxides, the anisotropy of 

coordination polyhedra was controlled by conjugated sub-

stitution of the cationic positions of Ln and 3d-metals, the 

shape and particle size distribution of crystallites were 

formed using the precursor method for the synthesis of ul-

trafine powders and subsequent thermobaric treatment. 

2. Experimental  

For the formation of single-phase solid solutions of the 

composition La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu), we em-

ployed the precursor synthesis method described in detail 

in [6] using 2-substituted ammonium citrate (C6H14N2O7). 

La(NO3)3∙6H2O, CaCO3, NiO, CoO and CuO of the “extra 

pure” qualification were used as starting reagents. The ox-

ides and carbonates were dissolved in concentrated nitric 

acid, and the nitrates – in distilled water. The solutions 

were mixed, and a 1.5-fold excess of the organic component 

was added. The resulting homogeneous solution was evap-

orated at 673 K until the reaction mixture ignited.  

Thermal treatment of the obtained pyrolysis product 

was carried out in two stages: at 873 K for 5 h to remove 

the residual organic products and at 1323 K for 16 h to com-

plete the phase formation process. The phase analysis of the 

reaction products was performed using the crystallographic 

database “Database of Powder Standard – PDF2” (ICDD, 

USA, Release 2009 [card 00-024-1326]). 

To form ceramic samples, the obtained single-phase finely 

dispersed black powder was pressed at a pressure of 9.5 MPa 

into tablets 10 mm in diameter and sintered at 1523 K for 8 h. 

The composition of the obtained samples was controlled 

using a Shimadzu XRD-7000 S automatic diffractometer 

with 0.03° step in the 10–120° range with 3–5 s exposure 

per point. X-ray pattern processing was performed with a 

FULLPROF-2019 program. The shape and average size of 

particles of the samples under investigation were deter-

mined by scanning electron microscopy on a JEOL JSM 6390 

scanning electron microscope with an attachment for en-

ergy dispersive analysis of JED 2300 in the BES mode at a 

x3000 magnification. 

The determination of the thermal expansion coefficient 

of the samples under study was carried out on a 

Netsch DIL 402 C dilatometer in an argon atmosphere. The 

maximum temperature was 1720 K. 

The measurements of oxygen content in the obtained 

specimens were carried out by thermogravimetry (TG) 

technique with the use of a TG-92 Setaram analyzer. For the 

thermal analysis, about 0.2 g of the pulverized material was 

placed in the corundum pan, heated, and kept in air at 

1223 K for 2 h. Then the sample was slowly cooled down to 

423 K with the rate of 1°/min. Such preliminary procedure 

is believed to provide a total removal of surface adsorbates 

and to achieve equilibrium values of oxygen content in ox-

ides in the cooling mode. Then the atmosphere was 

switched to Ar diluted by 5 vol.% H2 and the samples were 

heated up to 1223 K until an exhaustive oxygen loss was 

achieved. Such procedure resulted in the reduction of the 

sample to the powder mixture of La2O3, CaO, Co and Cu. The 

respective weight loss was used for calculations of the total 

oxygen content (4±δ) in the as-synthesized samples. 



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Thermobaric treatment of ceramic samples was carried 

out in a “toroid” high-pressure chamber on a DO-137A press 

at a pressure of 2.5 and 4 GPa for 5 minutes at 1173 K. To 

prevent carbon contamination of the sample, the internal 

walls of the heater were covered with platinum foil. 

Dielectric characteristics were measured using a univer-

sal analyzer of the frequency response of an impedance me-

ter/dielectric spectrometer Solartron 1260A functioning in 

the frequency range 1 mHz–30 MHz. The frequency depend-

ence of the dielectric constant was estimated in the fre-

quency range from 1 kHz to 1 MHz.  

Temperature examinations of electrical characteristics of 

samples in the range 10–300 K were carried out in pure he-

lium atmosphere in an autonomous closed cycle cryostat with 

the DE-204SL two-stage cryorefrigerator, based on Gifford-

Macmagon cycle using a helium water-cooled compressor. The 

accuracy of cryogenic temperature measurements was 0.2 K. 

3. Results and Discussion 

3.1. Synthesis and structural characteristics of complex 

oxide La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu). Micro-

structural analysis of the obtained ceramic samples 

For the synthesis of powdered oxides of the 

La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) composition, the "solu-

tion combustion" method was used [20–22]. The choice of 

diammonium citrate as an organic component ensures the 

formation of citrates of the corresponding metals and the 

release of NH4NO3 into the reaction zone [19]. The interac-

tion of ammonium nitrate with organic components of the 

reaction mixture provides the ignition of the solution, ac-

companied by decarboxylation. 

Pyrolysis of a reaction mass containing nitrogen in a re-

duced form proceeds with the formation of nanodispersed 

powders with a developed surface and high reactivity [23]. 

The high dispersion of the studied powders contributes to 

better sintering of ceramics and the absence of through and 

closed pores. 

Figure 1 illustrates the results of thermogravimetry exper-

iments. As can be seen, the studied oxides start to lose oxygen 

at 550 K and 650 K for the copper- and cobalt-doped samples, 

respectively. Earlier, a mechanism for the reduction of the 

copper-containing nickelate was considered in the literature 

[24–26] where two steps were also observed. The first one is 

related to the formation of the stoichiometric phase. At higher 

temperatures, deeper decomposition takes place, resulting in 

the formation of metals and simple oxides. XRD analysis of the 

reduced mixtures fully supports this point of view. 

It is important that the studied oxides remain stable in 

Air media where negligible changes in oxygen content are 

observed. At the same time, the cobalt-containing sample is 

characterized by elevated oxygen content compared with 

copper doped one which may indicate the formation of 

more oxidized forms such as Co3+. 

To determine the effect of particle morphology on die-

lectric properties, the formation of ceramics was carried 

out in two ways: heat treatment of the precursor in the air 

and thermobaric treatment (TBT) of the precursor. 

3.1.1. Heat treatment of the precursor in the air 

Figure 2 shows the dilatometric measurement data for the 

obtained powder samples. It can be seen from the plots that 

the sintering process of both samples begins at a tempera-

ture in the range from 1155 K to 1280 K. 

Figure 3 shows SEM images of ceramics obtained after 

heat treatment at 1523 K. The countable size distribution of 

crystallites is presented in the form of a histogram (Figure 3 

(inset)) expressing the percentage of grains with sizes lying 

in these intervals. 

The surface of ceramic samples (Figures 3a and 3b) is 

densely sintered i.e. has no through pores. Crystallites of ce-

ramic samples in both cases have a poorly crystallized shape 

with a not clearly pronounced growth zone. However, the 

sample containing Co has a more faceted lamellar shape com-

pared to the sample containing Cu. The average crystallite 

size for both samples is about 3 μm. Nevertheless, it should 

be noted that in the ceramics with Co the particles are more 

dispersed than in the sample containing Cu. 

 
Figure 1 Variations of oxygen content in La1.8Ca0.2Ni0.8M0.2O4±δ 
(M = Cu, Co) measured in Air flow and Ar diluted by 5 vol.% H2. 

The represented data were collected in cooling and heating modes, 
respectively. 

 
Figure 2 Kinetic curves of sintering complex oxides of 
La1.8Ca0.2Ni0.8M0.2O4±δ (M = Cu, Co) composition. 



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Figure 3 SEM micrographs of the La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co (a), 
Cu (b)) ceramics surface obtained after heat treatment (sintering) 
(the inset shows the crystallite size distribution). 

3.1.2. Thermobaric treatment (TBT) of the precursor 

Significant changes in the morphology of ceramics are 

observed after treatment of precursors simultaneously 

with temperature and pressure (TBT) (Figure 4). The 

morphology of crystallites changes significantly, acquir-

ing a more faceted shape, and the particle size decreases 

for both samples by approximately a factor of 2 (Figure 4 

(insets)). 

The influence of the morphology of ceramics after TBT 

on the dielectric properties and the regularities of changes 

in the shape of crystallites are poorly studied. In [27] the 

effect of TBT on ceramics with the composition CaCu3Ti4O12 

leads to an increase in the particle size and to the absence 

of a visible change in grain morphology. In contrast, after 

TBT in the La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) compounds 

the ceramic grain morphology changes rather strongly (Fig-

ure 4 (a) and (b)). It can be assumed that the shape and size 

of crystallites after TBT depend on the type of crystal lattice 

of the compound under study. 

The phase composition of the obtained ceramic samples 

was determined based on the results of X-ray phase analy-

sis (Figure 5).  

 
Figure 4 SEM micrographs of the La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co (a), 
Cu (b)) ceramics surface obtained after TBT (the inset shows the 
crystallite size distribution). 

The results of phase analysis of the obtained ceramic indi-

cate the absence of foreign phases; this is proven by the corre-

spondence of the X-ray diffraction reflections with the Miller in-

dices (hkl) of the structure of the Ruddlesden–Popper phase. 

Since, in oxides with a structure of the K2NiF4 type, there 

is a correlation between the dielectric properties and distor-

tion of the antiprisms of AO9 and octahedra BO6 [17, 28, 29], 

the crystal chemical parameters of all the samples under 

study were determined. Table 1 shows the crystallochemical 

parameters of the test compounds before and after TBT.  

To analyze the structural distortions of the compounds 

under study before and after TBT, Figure 6 shows a graph of 

normalized bond lengths, i.e., the ratio of the experimental 

interatomic distances to the theoretical sum of ion radii (ac-

cording to Shannon [30]) in the corresponding coordination 

(lexp/ltheor). The coordination polyhedra (La,Ca)O9 and 

(Ni,M)O6 are shown in the crystal structure (Figure 7). 

According to the literature date [27, 31], thermobaric 

treatment at temperatures up to 1200 K does not lead to a 

change in the space group of crystalline substances. How-

ever, structural deformation can occur, which can have a 

significant effect on material properties, such as magnetic 

or electrical. 



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Figure 5 Theoretical and experimental diffraction patterns of the 
La1.8Ca0.2Ni0.8M0.2O4+δ (M = Cu (a), Co (b)) ceramics obtained before 
and after thermobaric treatment. The Bragg reflections positions 

are marked with dashes. 

According to the data obtained (Figure 6), the strongest 

structural change after TBT is manifested along the c axis 

(the La (Ca)–O2b bond in the AO9 coordination polyhedron 

and the Ni(M)–O2b bond in BO6) for both samples. However, 

it is important to note that in the case of the sample contain-

ing Cu in position B (sample II'), the BO6 octahedron becomes 

more distorted, while the sample containing Co, on the con-

trary, after TBT, approaches the ideal lattice state. 

According to [32] the presence of Jahn-Teller ions in the 

composition of perovskite-type oxides provides the greatest 

response of structural distortions to thermobaric action. 

3.2. Temperature dependences of the electrical prop-

erties of materials at different frequencies 

The impedance hodographs (Figure 8) are the arcs of sem-

icircles whose ReZ intercepts correspond to the resistance 

of grain boundaries. 

The impedance hodographs for samples in all temperature 

range are arcs of semicircles, the radii of which monotonously 

decrease with increasing temperature, which indicates a de-

crease in electrical resistance of the grain boundaries.  

 
Figure 6 Normalized bond lengths values in coordination polyhedra 
(La,Ca)O9 and (Ni,M)O6 of the composition La1.8Ca0.2Ni0.8M0.2O4+δ 
(M = Co (I), Cu (II)) compounds, where I’ and II’ – samples after 

TBT at P = 2.5 GPa. 

 
Figure 7 Crystallographic structure of La1.8Ca0.2Ni0.8Co0.2O4+δ. The 
La and Ca atoms are represented by purple, Ni and M – by dark 
blue, oxygen – by red spheres. 

The presence of one arc on the impedance hodographs 

of the studied materials indicates that the processes occur-

ring in an alternating field can be characterized by a single 

relaxation time or that the relaxation times of carriers and 

polarization relaxation processes are distributed in a cer-

tain narrow interval. 

The frequency dependences of the imaginary part of 

the electric modulus for the studied samples at some tem-

peratures are shown in Figure 9 (for 

La1.8Ca0.2Ni0.8Cu0.2O4+δ samples) and Figure 10 (for 

La1.8Ca0.2Ni0.8Co0.2O4+δ samples). The polarization relaxa-

tion time (τ) was determined using the frequency values 

fmax corresponding to the maximum point of the graph 

ImM(f) plot using the equation: 

τ = 1/2π𝑓𝑚𝑎𝑥. (1)  

 



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Table 1 Crystallo chemical parameters of La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co (I), Cu (II)) samples (space group I4/mmm, La/Ca (0, 0, z), 
Ni/M (0, 0, 0), O(1) (0, 0.5, 0); O(2) (0, 0, z)). 

Samples I I’ (2.5 GPa) II II’ (2.5 GPa) 

Unit cell parameters 

a = b, Å 3.8552(2) 3.8580(2) 3.8257(4) 3.8328(1) 

c, Å 12.5546(3) 12.5208(7) 12.7156(1) 12.7212(3) 

V, Å3 186.591(4) 186.363(8) 186.110(7) 186.881(2) 

Atom coordinates 

La (Ca)     

z 0.3611(8) 0.3631(5) 0.3621(4) 0.3619(2) 

O1     

Occupancy 0.929(3) 0.902(8) 0.993(8) 0.889(6) 

О2     

z 0.1740(7) 0.1715(9) 0.1757(8) 0.1788(1) 

Occupancy 0.946(4) 1.086(7) 1.018(6) 1.090(3) 

χ2 0.781 0.937 0.785 0.892 

Interatomic distances, Å 

Ni/M–O1(x4) 1.9276(8) 1.9290(6) 1.9128(6) 1.9164(2) 

Ni/M–O2b(x2) 2.186(7) 2.147(3) 2.234(4) 2.276(1) 

La/Ca–O1(x4) 2.5988(7) 2.5806(12) 2.5946(12) 2.5990(17) 

La/Ca –O2a(x4) 2.7617(3) 2.7622(6) 2.7481(2) 2.7573(3) 

La/Ca –O2b(x1) 2.348(6) 2.399(3) 2.371(4) 2.379(7) 

Rf-factor 3.98 4.32 3.40 2.65 

GII 0.3909 0.8723 0.5561 0.6720 

 
Figure 8 Impedance spectra of cells with samples La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) (a, c) compounds before and after TBT at 
P = 2.5 GPa (b, d).



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Figure 9 The frequency dependences of the imaginary part of the electric modulus for the La1.8Ca0.2Ni0.8Cu0.2O4+δ samples (before (a, c) 

and after TBT (b, d)) at some temperatures and frequency dependences of the imaginary part of the impedance at T = 100 K. 

The relaxation times of charge carriers from –ImZ(f) at 

T = 100 K (Figure 9) are  = 5.010–6 s and = 1.110–5 s (for 

before and after TBT, respectively). 

For the material with copper, the relaxation times 

τ = 1/2π𝑓𝑚𝑎𝑥 after TBT slightly increase, but for the mate-

rial with Co, the values  decrease by an order of magnitude 

and even by two at 𝑇 ≤ 100 K. 

An increase in the relaxation time after TBT can be as-

sociated with an increase in polarization in the regions of 

grain boundaries, the surface of which increases with a de-

crease in the particle size during such treatment. That is, 

the external causes described in the IBLC model and asso-

ciated with the Maxwell-Wagner polarization mechanism 

play a large role in increasing the dielectric constant. 

3.3. Dielectric properties of La1.8Ca0.2Ni0.8M0.2O4+δ 

(M = Co, Cu) ceramics 

The relative complex permittivity, admittance and loss tan-

gent were estimated by measuring the impedance  

Z = Re Z + i ImZ with the equation: 

∗(𝜔) =
𝑙

𝑆

1

𝑖𝜔 0𝑍
∗(𝜔)

, 
(2) 

𝑌∗(𝜔) =
1

𝑍∗(𝜔)
, 

(3) 

tan 𝛿(𝜔) =
Im 

Re 
, 

(4) 

where  is the circular frequency (ω = 2π𝑓, and 𝑓 is the lin-

ear frequency of electric field), 0 is the dielectric constant 

of vacuum, and 𝑙 and S are the sample thickness and the 

surface area contacting with one electrode, respectively. 

3.3.1. Dielectric characteristics of the test samples obtained 

after heat treatment in air  

The plots of the dependence of the dielectric constant and 

the dielectric loss angle tangent of the 

La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) ceramics on the fre-

quency at different temperatures are shown in Figure 11. 

The dielectric constant for both samples have high val-

ues of the order of 103 (M = Co) and 8∙102 (M = Cu) and is 

frequency independent in the temperature range from 100 

to 260 K. However, low values of the dielectric loss tangent 

are observed only in the temperature range of 100–120 K.  



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Figure 10 The frequency dependences of the imaginary part of the electric modulus for the La1.8Ca0.2Ni0.8Co0.2O4+δ samples (before (a, c) 
and after TBT (b, d)) at some temperatures and frequency dependences of the imaginary part of the impedance at T = 160 K. 

The appearance of sufficiently high values of the dielec-

tric constant can be due to both external factors (near-elec-

trode polarization effects, Maxwell-Wagner effects on grain 

boundaries, the influence of shape and size of grains) and 

internal reasons (properties of the material itself – features 

of the crystalline layered structure, type of charge carriers 

and related polarization processes). 

3.3.2. Dielectric characteristics of the ceramics obtained 

after thermobaric treatment 

The resulting dielectric data for the ceramics after TBT are 

shown in Figure 12. Both samples are characterized by an 

increase in Re ε  and retention of frequency and tempera-

ture independence (in comparison with the ε value after the 

ceramics heat treatment). For the sample containing Cu in 

position B, the value of the dielectric constant increases by 

200, and for M = Co – increases by 100. 

The dielectric constant of the La1.8Ca0.2Ni0.8Cu0.2O4+δ ce-

ramic increases significantly after thermobaric treatment 

from 600 to 2000. For the La1.8Ca0.2Ni0.8Co0.2O4+δ sample, 

the change in the dielectric constant increases from 1000 to 

2000). The difference is due to a stronger distortion of the 

BO6 tetrahedron in the copper-containing sample, which 

due to the influence of the Jahn-Teller effect. 

Also , an increase increasing in the dielectric constant of 

La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) ceramic after TBT can 

be associated with a change in the morphology of crystal-

lites that acquire regular geometric flat surfaces after TBT 

(Figure 4), with a decrease in the average grain size 

(from ~3 μm to ~1.7 μm). As a consequence, this leads to 

more pronounced polarization effect in the region of grain 

boundaries with an increased total area of grain boundaries 

(IBLC model) [33, 34], and with an increase in the number of 

barriers for charge carriers in the form of surfaces of inho-

mogeneities, the number of which increases in the course of 

TBT. Thus, the increase in the values of the dielectric con-

stant observed in the materials after TBT is mainly associ-

ated with the Maxwell-Wagner mechanism of polarization at 

grain boundaries and inhomogeneities.  

4. Conclusions 

New complex oxides of the K2NiF4 type with the 

La1.8Ca0.2Ni0.8M0.2O4+δ (M = Co, Cu) composition were syn-

thesized by pyrolysis of nitrate-organic compositions with 

2-substituted ammonium citrate as an organic component, 

proceeding in the "solution combustion" mode.  

 



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Figure 11 The frequency dependence of dielectric constant and die-
lectric loss tangent on temperature for La1.8Ca0.2Ni0.8M0.2O4+δ 
(M = Cu (a), Co (b)) ceramics obtained after heat treatment in air. 

The transformation of the resulting precursors into the 

final product takes place at lower temperatures (1223 K) 

compared to the solid-phase method (1473 K), which solves 

the problem of obtaining nanodispersed single-phase sam-

ples for the manufacture of gas-tight ceramics. 

To obtain ceramic samples based on these precursors, 

two methods were used: thermal treatment in air and ther-

mobaric treatment (TBT). During the formation of ceramic 

samples, the stage of obtaining nanodispersed single-phase 

powders of the required composition makes it possible to 

separate two processes that run in parallel during the solid-

phase synthesis – phase formation and sintering. The nano-

dispersion of the powder of an already prepared composi-

tion ensures the production of dense ceramic samples, the 

sintering of which requires much less time than the sinter-

ing of the samples produced by the solid-phase synthesis. 

A study of the influence of methods for obtaining ceram-

ics on the morphology of the obtained samples was carried 

out. A decrease in the average grain size after TBT was 

found to be almost twofold in comparison with ceramics ob-

tained by sintering in an air atmosphere. The geometric 

shape of the grains also undergoes significant changes, be-

coming more faceted. 

 
Figure 12 The frequency dependence of dielectric constant and die-
lectric loss tangent on temperature for La1.8Ca0.2Ni0.8M0.2O4+δ 
(M = Cu (a), Co (b)) ceramics obtained after TBT. 

Two reasons for the increase in the dielectric constant 

of ceramic samples after TBT were identified. The first one 

is the distortion of the AO9 and BO6 coordination polyhedra, 

which is most pronounced along the с axis. A significant in-

crease in the Ni(M)–O2b bond length, for example, in the 

case of the sample containing Cu leads to a noticeable in-

crease in Reε from 600 to 2000. The second reason lies in 

the increasing the permittivity with decreasing crystallite 

size, due to the influence of grain boundary effects resulting 

from the Maxwell-Wagner polarization mechanism. 

Supplementary materials 

No supplementary materials are available. 

Funding 

This work was supported by the Russian Foundation for 

Basic Research (RFBR) (grant no. 20-33-90239), 

https://www.rfbr.ru/rffi/eng. 

 

https://www.rfbr.ru/rffi/eng


Chimica Techno Acta 2022, vol. 9(4), No. 20229410 ARTICLE  

10 of 11 

Acknowledgments 

The authors are grateful to the Leading Researcher of the 

Laboratory of Oxide Systems of the Institute of Solid State 

Chemistry UB RAS Leonidov Ilia Arkadievich for the discus-

sion of the results.  

Author contributions 

Conceptualization: D.Y.A., C.T.I. 

Data curation: M.N.V. 

Formal Analysis: D.Y.A, M.N.V. 

Funding acquisition: D.Y.A. 

Investigation: D.Y.A., M.A.A.,  

Methodology: D.Y.A., M.A.A., S.A.Y., K.N.I. 

Project administration: D.Y.A. 

Resources: D.Y.A., C.T.I. 

Software: D.Y.A., M.A.A.  

Supervision: C.T.I., L.I.A. 

Validation: D.Y.A., C.T.I., M.N.V. 

Visualization: D.Y.A. 

Writing – original draft: D.Y.A. 

Writing – review & editing: C.T.I., M.N.V., L.I.A. 

Conflict of interest 

The authors declare no conflict of interest. 

Additional information 

Author IDs: 

Yulia A. Deeva, Scopus ID 57208866603; 

Abdullo A. Mirzorakhimov, Scopus ID 57133042800; 

Alexey Yu. Suntsov, Scopus ID 26536695400; 

Nadezhda I. Kadyrova, Scopus ID 6701574610; 

Nina V. Melnikova, Scopus ID 7003907528; 

Tatyana I. Chupakhina, Scopus ID 6602115793. 

 

Websites: 

Ural Federal University, https://urfu.ru/en; 

Institute of Solid State Chemistry UB RAS, 

https://www.ihim.uran.ru. 

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