Synthesis, structure and electrical properties of Mg-, Ni-codoped bismuth niobates 231 D O I: 1 0. 15 82 6/ ch im te ch /2 01 7. 4. 4. 04 M.S. Koroleva, I.V. Piir, E.I. Istomina Institute of Chemistry Komi SC UB RAS 48 Pervomayskaya St., Syktyvkar, 167982, Russian Federation e-mail: marikorolevas@gmail.com Synthesis, structure and electrical properties of Mg-, Ni-codoped bismuth niobates Mg-, Ni-codoped bismuth niobates Bi 1.6 Mg 0.8–x Ni x Nb 1.6 O 7–δ (x = 0; 0.2; 0.4; 0.6; 0.8) were obtained by conventional solid-state reaction method. It was shown that the Mg atoms are distributed at the Nb sites while the Ni atoms are distributed over the Bi- and the Nb-sites, according to the results of compari- son of pycnometric and X-ray density of the Bi 1.6 Mg 0.4 Ni 0.4 Nb 1.6 O 7–δ pyrochlore. In this case, about 15–20% of the vacancies are formed at the Bi sites. The obtained compounds are stable up to their melting point based on the DSC analysis data. Real dielectric permittivity ε' of the Bi 1.6 Mg 0.8–x Ni x Nb 1.6 O 7–δ sam- ples decreases from 80 to 65 with the temperature decrease from 25 to 700 °C and practically does not depend on frequency in the range of 1–1000 kHz. Oxi- des Bi 1.6 Mg 0.8–x Ni x Nb 1.6 O 7–δ behave like insulators up to 280 °C, their conductivi- ty increases with temperature (E a,dc ≈ 1.3 eV, dc) and with the Ni content at a given temperature. Keywords: pyrochlore; Bi 1.6 Mg 0.8–x Ni x Nb 1.6 O 7–δ ; dopant distribution; dielectric behavior; elec- trical conductivity. Received: 14.11.2017; accepted: 12.12.2017; published: 25.12.2017. © Koroleva M.S., Piir I.V., Istomina E.I., 2017 Koroleva M.S., Piir I.V., Istomina E.I. Chimica Techno Acta. 2017. Vol. 4, No. 4. P. 231–241. ISSN 2409–5613 Introduction Ceramics in the Bi2O3-MxOy- Nb2O5 ternary system are interesting from the perspective of their dielectric proper- ties. The most attention has been paid to the Zn-, Mg-containing bismuth niobates, which possess high dielectric constant (170–180) and low dielectric loss (~10-4) at 1 MHz (at room temperature) [1–9]. To search for the same properties Fe- [10], Mn- [11–12], Co- [13], Ni- [12, 14–15], Cu- [12] and the mixed Zn-M (M – Sr [16], Ca [16–17], Mn [16, 18], Ti [19–22], Sn [19, 22], Zr [19, 21–22], Ce [19,22], Gd [21], Ta [23], La [24]), Mg-M (M – Sr [25], Nd [26], Cu [27]) bismuth niobates and other ones were synthesized. The im- proved permittivity was achieved by Ti doping of the Nb sites in the pyrochlore structure [21–22] and by Cu doping in Bi1.5CuxMg1-xNb1.5O7 (x = 0.075) [27]. In most cases, doping leads to the permit- tivity decrease and to the tangent loss in- crease. However, electrical properties of several systems were investigated in the high temperature range (up to 700  °C) only in order to determine their conduc- tivity mechanism [3, 9, 19–20, 27]. In our previous work [28–29] we have deter- mined that the dielectric constant of the Bi1.6CuxMg0.8-xNb1.6O7-δ pyrochlores behave 232 unusually passing through a maximum (250–350 °C) with temperature increas- ing. The value of the dielectric constant at the maximum is very high: ~106 (100 Hz). Second-type phase transition was found at 200 °C. To establish the reasons for such behavior, the distribution of doped me- tals in the cation (A–, B–sites) positions in the pyrochlore structure (A2B2O6O’, the space group Fd3m (No 227)) was studied by X-ray diffraction pattern refinement (Rietveld analysis), and by comparison of pycnometric density with the calculated one. It has been determined that the elec- tronegativity plays the crucial factor for the distribution of the Mg atoms in the Nb sites and the Cu atoms – in the Bi and the Nb sites in equal ratios. In any case, there are 10–15% of vacancies in the Bi sites. In accordance with the other systems’ investi- gations, the vacancy concentration always remains at about 5–10% in the Bi sites in the pyrochlore structure [4, 10–11, 14, 30]. In this work we have a goal to deter- mine a distribution of Ni and Mg dopants in the pyrochlore structure and investigate the temperature dependence of electrical properties of the Bi1.6Mg0.8-xNixNb1.6O7-δ. Experimental Mixed bismuth niobates Bi1.6Mg0.8-xNixNb1.6O7-δ (x = 0; 0.2; 0.4; 0.6; 0.8) were prepared by a conventional solid state reaction method [31–32] from the oxides with high degree of purity (>99.9%): Bi2O3, NiO, MgO, Nb2O5. The oxides were weighted in an appropriate ratio (Bi2O3:MgO:NiO:Nb2O5 = 0.8:(0.8- x):x:0.8), grinded, pressed into pellets and calcined at 650 °С (8 h), 850 °C (6 h), 900 °C (6 h), 950 °C (12 h), 1000 °C (6 h), 1050  °C (12 h), 1070 (6 h), and 1100 °C (11 h) consequently in corundum cruci- bles. The annealing at 650 °C was carried out in order to avoid significant bismuth weight loss and the melting stage of Вi2О3 at 824  °C. As the temperature and dura- tion of the calcination increased, the im- purity phase content decreased. After each firing step, the pellets were regrinded for 30 min and repressed. The pellets’ diame- ter and thickness varied from 12 to 14 mm and from 2.2 to 2.7 mm, respectively. The phase composition of the samples was examined by powder X-ray diffrac- tion method on a SHIMADZU XRD-6000 diffractometer using Cu Kα emission within the angle range 10–80° (the step – 0.05°). Distribution of nickel and magne- sium atoms in the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ pyrochlore was determined by Rietveld analysis (FullProf software package [33]). Scanning electron microscopy (SEM) was carried out on a TESCAN VEGA 3 SBU microscope. The local composition of the samples was studied on polished pellets by energy dispersion spectroscopy (EDS). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TG) of Bi1.6Mg0.4Ni0.4Nb1.6O7-δ powder were car- ried out in the air in platinum crucibles with heating up to 1300 °C and a heating rate of 5 °C/min (NETZSCH STA 409 PC/ PG). The electrical measurements were performed on the pellets, both sides of which were coated uniformly with a  sil- ver paste. Capacitance and dielectric loss tangent were measured by MT–4090 LCR meter in different gases (air, p(O2) = 0.21 atm and oxygen, p(O2) = 0.99 atm) at four frequencies (1, 10, 100, 200 kHz) in the temperature range of 25–750  °C. The impedance plots were measured by im- mittance meter E7-28 at 0.5 V in the tem- perature and frequency ranges 25–700 °C and 24 Hz – 10 MHz, respectively. The 233 electrical data were collected after 10 min after the thermal equilibrium was reached. The thermoelectric effect – Seebeck coeffi- cient – was determined in the temperature range 130–330 °C in a temperature gradi- ent of 30–40 °C across the material. Results and discussion Synthesis and Characterization The XRD patterns of Bi1.6Mg0.8-xNixNb1.6O7-δ (0 ≤ x ≤ 0.8) are shown in Fig. 1. The pyrochlore structure is formed for the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ com- position only. The small amounts of second phases, identified as MgNb2O6 (Pbcn space group) and as NiNb2O6 (Pbcn space group), were found in the samples with x = 0; 0.2 and with x = 0.6; 0.8, respectively. The surfaces of the Bi1.6Mg0.8-xNixNb1.6O7-δ (0 ≤ x ≤ 0.6) pol- ished pellets after the last calcination are shown in the SEM images (Fig. 2a–2c). According to the EDS data, the presence of additional phases such as MgNb2O6 (at x = 0) or as mixed Mg-Ni contain- ing niobates (at x = 0.2; 0.6) can be seen. The amount of impurities is around 5%. The local compositions of the main and second phases are presented in the cap- tion to Fig. 2. The composition of the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ ceramic deter- mined by EDS is Bi1.60Mg0.38Ni0.45Nb1.6O7-δ, which is close to the desired composition. The porosity of the pellets was around 35– 40%, as estimated from SEM micrographs. DSC and TG curves of the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ powder are shown in Fig. 3. The endothermal effect was found on the DSC curve at 1261 °C. This effect may be associated with the melting of the sample. The reason for the weight rise during the heating process has not been established yet. It may be related to the partial oxidation of Ni+2 to Ni+3. The Rietveld refinement of the XRD pattern of Bi1.6Mg0.4Ni0.4Nb1.6O7-δ was car- ried out. The occupations of atom sites were fixed in accordance with the quan- titative composition of the compound. The possibility of displacement of the bismuth atoms (from 16c sites to 96h or 96g sites) and the oxygen atoms O′ as- sociated with bismuth (from 8a sites to 32e sites) were considered, like in [Bi0.833 Mg0.11□0.04]2[Mg0.24Nb0.76]2O7 and in [Bi0.833 Ni0.125□0.04]2[Ni0.25Nb0.75]2O7 pyrochlores [14]. Various models were studied to de- termine the distribution of doped atoms in the cation (Bi, Nb) sites of the pyro- chlore structure. Among the alternative models that were considered there are [Bi1.56Ni0.34□0.10][Ni0.05Mg0.39Nb1.56]O7.02 and [Bi1.56Mg0.34□0.10][Mg0.05Ni0.39Nb1.56]O7.02. In these models 5% of vacancies remain at the Bi sites. The distribution of dopant atoms in equal ratio among two different cation sites causes formation of about 2.5% vacant sites both in the Bi and Nb sublat- tices. It is not typical for the pyrochlore structure. The best agreement between theoretical and observed X-ray patterns was obtained for the model designated as Fig. 1. X-ray diffraction patterns of Bi1.6Mg0.8-xNixNb1.6O7-δ (0 ≤ x ≤ 0.8) 10 20 30 40 50 60 70 80 0 10 20 30 40 80 0 55 3, 73 1 64 242 2 62 0 53 3 62 2 44 4 55 1, 71 1 66 2 66 0, 82 2 64 4 22 0 31 1 2 22 40 0 33 1 33 3 44 0 53 1 11 1 * I 1 03 , c ps ∆ ∆ * - MgNb2O6 ∆ - NiNb2O6 * 0.8 0.2 0.4 0.6 0.0 2θ, deg. x 234 [Bi1.56Ni0.34□0.10][Ni0.05Mg0.39Nb1.56]O7.02. In this model, all Mg atoms are distributed over the Nb sites. Several models were considered with different vacancy concen- trations (10–25%) in the Bi sites and Mg atoms occupying the Nb sites. The best values of Rwp (%), Rp (%), χ 2 factors can be obtained for the models with 15–20% vacancies in the Bi sites. The refined crystallographic parameters of the [Bi1.46Ni0.18□0.36][Ni0.18Mg0.36Nb1.46]O6.52 model are presented in Table 1. This mo- del corresponds to the equal distribution of Ni atoms in the Bi and the Nb sites, whereas 18% of vacancies remain in the Bi sites. Displacement of Bi and Ni atoms (16c Fig. 2. SEM images of Bi1.6Mg0.8-xNixNb1.6O7-δ samples: a – x = 0 (1 – Bi1.72Mg0.78Nb1.6O7-δ, 2 – MgNb2O6); b – x = 0.2 (1 – Bi1.60Mg0.44Ni0.18Nb1.6O7-δ, 2 – Mg0.85Ni0.11Nb2O6); c – x = 0.4 (Bi1.60Mg0.38Ni0.45Nb1.6O7-δ); d – x = 0.6 (1 – Bi1.68Mg0.16Ni0.56Nb1.6O7-δ, 2 – Mg0.35Ni0.55Nb2O6) a b c d 235 to 96h sites) is observed. The observed, calculated and difference X-ray diffrac- tion profiles for the model are shown in Fig. 4. To our mind, the distribution of do- pant atoms in the cation sites is governed by the electronegativity values, apart from the ionic radii influence. So, Mg2+ and Ni2+ ionic radii are close (0.72 Å and 0.70 Å, respectively) [34]. The electronegativity of Mg (1.23) by Allred-Rochow [35] is equal to that of Nb (1.23), and the elec- tronegativity of Ni (1.75) is close to that of Bi (1.67). Obviously, the electronegativ- ity values impact on the dopant distribu- tion in the pyrochlore structure, like in the Cu–Mg substituted bismuth niobates [28–29]. The pycnometric density of the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ powder is 6.50±0.24 g/cm3. The calculated density for the [Bi1.56M0.34□0.10][M0.44Nb1.56]O7.02 model where M – the dopant metals (5% of va- cancies in the Bi sites) is 7.02 g/cm3. The calculated density for the model with 18% vacancies in the Bi sites ([Bi1.46M0.18□0.36] [M0.54Nb1.46]O6.52) is 6.53 g/cm 3 and is in agreement with the pycnometric density value. Thus assumed amount of about 15– 20% vacant sites in Bi sublattice seems to be in agreement with the experimental results obtained in the present study. Electrical properties Complex impedance plots of the Bi1.6Mg0.8-xNixNb1.6O7-δ ceramics were drawn from impedance spectroscopy data. The data were obtained during cooling from 700 to 160 °C to exclude proton con- ductivity. Perfect semicircles are traced in Fig. 4. Observed, calculated and difference X-ray diffraction profiles for [Bi1.46Ni0.18□0.36][Ni0.18Mg0.36Nb1.46]O6.52 Fig. 3. DSC and TG curves of Bi1.6Mg0.4Ni0.4Nb1.6O7-δ 0 200 400 600 800 1000 1200 -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 1261 °CT, DSC, W/g TG, % 100 102 104 106 108 110 Table 1 Refined crystallographic parameters for Bi1.6Mg0.4Ni0.4Nb1.6O7-δ (space group Fd3m) Atom type Site x y z Biso, Å 2 Occupation [Bi1.46Ni0.18□0.36][Ni0.18Mg0.36Nb1.46]O6.52 Bi/Ni 96h 0 0.015 0.985 0.708 0.725/0.09 Nb/Ni 16d 1/2 1/2 1/2 0.003 0.725/0.09 Nb/Mg 16d 1/2 1/2 1/2 0.003 0.725/0.18 O 48f 1/8 1/8 0.428 0.010 1 O’ 8a 1/8 1/8 1/2 0.010 0.52 a = 10.5204 Å; Rp = 4.51%, Rwp = 5.86%, χ 2 = 2.22. 10 20 30 40 50 60 70 80 -2000 0 2000 4000 6000 8000 10000 Iobs Icalc Iobs-Icalc Bragg position In te ns ity , a rb . u ni ts 2θ, deg. 236 the temperature range 320–700 °C. At the temperature less than 320 °C half semicir- cles may be observed. In Fig. 5 impedance plots for the Bi1.6Mg0.8-xNixNb1.6O7-δ (x = 0.4; 0.6) ceramics are presented. The plots are well fitted by a single parallel RC ele- ment (inset of Fig. 5) where R and C be- long to bulk resistance and capacitance, respectively [36–38]. The measured pa- rameters are listed in Table 2. Permittivity recalculated from the ca- pacitance values for the samples with Ni content x = 0.20, 0.40, and 0.60 is (70–81), (70–81), and (65–76), respectively, for the temperature range of 700–280 °C. Cal- culated permittivity does not depend on the frequency in the range of 1–1000 kHz and is close to the dc permittivity values. At room temperature, the permittivity is around 80 in the frequency range of 1–1000 kHz. All ceramics under inves- tigation behave like a dielectric (tan δ ≈ 0.002) up to 280 °С. Calculated from Arrhenius direct con- ductivity plots activation energy values are close to 1.2 eV (the third column in Table 3). These values are almost equal to ones at 1 kHz (the second column in Ta- ble 3). The corresponding Arrhenius con- Fig. 5. Complex impedance plots at 500, 600 and 700 °C for the Bi1.6Mg0.8–xNixNb1.6O7–δ ceramics with x = 0.4; 0.6 0 50000 100000 150000 200000 250000 0 50000 100000 150000 200000 170.2 kHz 24 Hz 22.2 kHz Z ', Ω -Z '', Ω 500 oC 600 oC 700 oC 0 10000 20000 30000 40000 50000 0 10000 20000 30000 662 kHz Z', Ω 500 oC 600 oC 700 oC -Z'', Ω 86.3 kHz a b Table 2 Rb and Cb parameters of the RC elements in the temperature range 280–700 °C for the Bi1.6Mg0.8–xNixNb1.6O7–δ ceramics T, °C x = 0.20 (h = 0.265 cm; d = 1.280 cm) x = 0.40 (h = 0.235 cm; d = 1.300 cm) x = 0.60 (h = 0.220 cm; d = 1.325 cm) R, kΩ C, pF R, kΩ C, pF R, kΩ C, pF 280 (79±3)·104 34.77±0.08 (50±3)·104 40.61±0.18 (111.7±2.7)·103 42.03±0.26 320 (157.8±2.5)·103 34.32±0.11 – – (173±3)·102 41.4±0.3 360 (373±4)·102 33.99±0.15 (310±4)·102 39.77±0.20 2860±30 40.8±0.3 400 9420±60 33.57±0.14 7560±40 39.18±0.12 606.8±2.4 39.97±0.15 500 558.5±2.3 32.41±0.14 164.4±0.5 37.87±0.12 49.61±0.08 38.66±0.09 600 62.8±0.4 31.08±0.28 21.52±0.04 36.57±0.13 8.460±0.014 37.36±0.14 700 8.972±0.026 29.88±0.19 4.032±0.010 35.22±0.24 1.913±0.004 35.8±0.3 237 ductivity plots at 1 kHz for all ceramics are shown in Fig. 6a. The activation energy values, which are greater than 1 eV, may be associated with ionic conduction. The same activation energy values (~1.27 eV) are known for the (Bi1.5Zn0.5)(Nb0.5M1.5)O7 (M – Ti, Sn, Zr, and Ce) ceramics [19] at T > 350 °C with the ionic type of conduc- tivity. The conductivity dependences on the temperature for the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ ceramic (160–750 °C) in the air and in the oxygen atmosphere are shown in Fig. 6b. The conductivity of the ceramic does not dependent on the oxygen pressure, and the value of Seebeck coefficient is near 0 mV/K in the temperature range of 200– 340 °C. These data indicate that there is no impurity-caused conductivity. For all ceramics, an electrical modu- lus (M") maximum is detected on the logarithmic scale of frequency (Fig. 7), indicating the presence of a polariza- tion process. These relaxation effects are characterized by the full width at half maximum (FWHM) peaks of M"(f) be- ing ~ 1.2 decades. This value is close to an ideal Debye response (1.14 decades) that characterizes the ceramics as electrically homogenous. At frequencies of the M" maximum value the relaxation time was calculated (Fig. 7). Frequency values at M" maxima were plotted vs temperature in an Arrhenius-type fashion. Obtained ac- cordingly values of activation energy are a b Fig. 6. Electrical conductivities as functions of reciprocal temperature at 1 kHz: a – Bi1.6Mg0.8-xNixNb1.6O7-δ; b – Bi1.6Mg0.4Ni0.4Nb1.6O7-δ Table 3 Activation energies of (dc, ac) conductivity and relaxation process of the substituted bismuth niobate pyrochlores Compound Ea (conductivity, 1 kHz), eV Ea (conductivity, dc), eV Ea (relaxation), eV Bi1.6Mg0.8Nb1.6O7–δ 1.03±0.06 – – Bi1.6Mg0.6Ni0.2Nb1.6O7–δ 1.09±0.03 1.25±0.03 1.38±0.03 Bi1.6Mg0.4Ni0.4Nb1.6O7–δ 1.14±0.03 1.20±0.03 1.38±0.03 Bi1.6Mg0.2Ni0.6Nb1.6O7–δ 1.10±0.03 1.20±0.04 1.23±0.04 Bi1.6Ni0.8Nb1.6O7–δ 1.17±0.08 – – 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -10 -9 -8 -7 -6 -5 -4 -3 Ea = 1.03 ± 0.06 eV Ea = 1.136 ± 0.009 eV 0.80 0.60 0.40 0.20 0.00 lg σ, σ (S cm -1 ) 103T -1, K-1 0,8 1,0 1,2 1,4 1,6 1,8 -8 -7 -6 -5 -4 -3 1.11 eV 103T -1, K-1 lg σ, σ (S cm -1 ) air O2 238 close to the ones obtained from the Arrhe- nius conductivity plots (Table 3). It points out that the hopping-type conductivity is typical for the Bi1.6Mg0.8–xNixNb1.6O7–δ ceramics, like for Bi1.5ZnNb1.5O7 [36, 38] and Bi3.55Mg1.78Ta2.67O13.78 [37] pyrochlo- res with Ea (relaxation) are 0.94 eV and 1.37 eV, respectively. Conclusions Mixed Mg–, Ni–containing bismuth niobates Bi1.6Mg0.8-xNixNb1.6O7-δ (0 ≤ x ≤ 0.8) were synthesized by the conven- tional solid-state reaction method. For all samples the main crystal phase is the pyrochlore. The Bi1.6Mg0.4Ni0.4Nb1.6O7-δ ce- ramic is a single-phase compound and is stable up to its melting point (1261 ºC). Based on structural analysis and the com- parison of pycnometric and calculated densities of the Bi1.6Mg0.4Ni0.4Nb1.6O7-δ, it was found that Mg atoms are distributed over the Nb sites, Ni atoms are distrib- uted at the Bi and Nb sites almost in the equal ratio. In this case, there are about 15–20% vacant sites in the Bi sublattice. The Bi1.6Mg0.8-xNixNb1.6O7-δ ceramics are characterized by the hopping type of con- ductivity (Ea = 1.0–1.4 eV). It was deter- mined that dielectric permittivity varies from 81 to 65 as the temperature increases from 280 to 700 °C, and practically does not depend on frequency in the range of 1–1000 kHz. Acknowledgements This study received the financial support of Russian Foundation for Basic Research (project No. 15-03-09173 А). The study was performed using the equipment of the Center for Shared Use of Scientific Equipment “Khimiya” of the Institute of Chemistry, Komi Science Center, Ural Branch of the Russian Academy of Sciences. References 1. Nino JC, Lanagan MT, Randall CA. Dielectric Relaxation in Bi2O3–ZnO–Nb2O5 Cu- bic Pyrochlore. J Appl Phys. 2001;89(8):4512–6. DOI:10.1063/1.1357468. a b Fig. 7. Imaginary part of electrical modulus as a function of frequency for the Bi1.6Mg0.8-xNixNb1.6O7-δ ceramics at x = 0.4 (a), x = 0.6 (b) 101 102 103 104 105 106 107 0.000 0.002 0.004 0.006 τ σ = 2.14 10-4 s τ σ = 7.17 10-6 s τ σ = 9.36 10-7 s τ σ = 1.22 10-7 s 400 oC 500 oC 600 oC 700 oC M'' f, Hz 101 102 103 104 105 106 107 0.000 0.002 0.004 0.006 0.008 τσ = 1.84 10 -6 s τ σ = 6.19 10-8 s 400 oC 360 oC 320 oC 280 oC 700 oC 600 oC 500 oC f, Hz M'' 239 2. Liu W, Wang H. Enhanced dielectric properties of Bi1.5ZnNb1.5O7 thick films via cold isostatic pressing. J Electroceram. 2012;29:183–6. DOI:10.1007/s10832-012-9758-8. 3. Ren W, Trolier-Mckinstry S, Randall CA, Shrout TR. Bismuth zinc niobate pyro- chlore dielectric thin films for capacitive applications. J Appl Phys. 2001;89(1):767– 74. DOI:10.1063/1.1328408. 4. Levin I, Amos TG, Nino JC, Vanderah TA, Randall CA, Lanagan MT. Structural Study of an Unusual Cubic Pyrochlore Bi1.5Zn0.92Nb1.5O6.92. J Solid State Chem. 2002:168:69–75. DOI:10.1006/jssc.2002.9681. 5. Jiang SW, Li YR, Li RG, Xiong ND, Tan LF, Liu XZ, Tao BW. Dielectric proper- ties and tunability of cubic pyrochlore Bi1.5MgNb1.5O7 thin films. Appl Phys Lett. 2009;94:162908-1-162908-3. DOI:10.1063/1.3126442. 6. Xia W, Xue P, Wu H, Lu Y, Zhang Y, Zhou Sh, Zhu X. Dielectric properties and atomic-scale microstructural characterizations of cubic-pyrochlored ceramics in the system of Bi2O3-MgO-Nb2O5. J Alloys Compd. 2017;701:682-8. doi:10.1016/j.jall- com.2017.01.153. 7. Gao L, Jiang Sh, Li R, Li B, Li Y. Structure and dielectric properties of sput- tered bismuth magnesium niobate thin films. Thin Solid Films. 2012;520:6295-8. DOI:10.1016/j.tsf.2012.06.035. 8. Zhang Y, Zhu X, Zhou Sh, Zhu J, Liu Zh, Al-Kassab T. Atomic-scale microstruc- tural characterization and dielectric properties of crystalline cubic pyrochlore Bi1.5MgNb1.5O7 nanoparticles synthesized by sol–gel method. J Nanopart Res. 2014;16:2208. DOI:10.1007/s11051-013-2208-y. 9. Tan PY, Tan KB, Khaw CC, Zainal Z, Chen SK, Chon MP. Phase equilibria and di- electric properties of Bi3+(5/2)xMg2-xNb3–(3/2)xO14-x cubic pyrochlores. Ceramics Interna- tional. 2014;40:4237–46. DOI:10.1016/j.ceramint.2013.08.087. 10. Lufaso MW, Vanderah TA, Pazos IM, Levin I, Roth RS, Nino JC, Provenza- no  V, Schenck PK. Phase formation, crystal chemistry, and properties in the sys- tem Bi2O3–Fe2O3–Nb2O5. J Solid State Chem. 2006;179:3900–10. DOI:10.1016/j. jssc.2006.08.036. 11. Vanderah TA, Lufaso MW, Adler AU, Levin I, Nino JC, Provenzano V, Schenck PK. Subsolidus phase equilibria and properties in the system Bi2O3:Mn2O3±x:Nb2O5. J Solid State Chem. 2006;179:3467-3477. DOI: 10.1016/j.jssc.2006.07.014. 12. Sirotinkin VP, Bush AA. Preparation and Dielectric Properties of Bi1.5MNb1.5O7 (M = Cu, Mg, Mn, Ni, Zn) Pyrochlore Oxides. Inorg Mater. 2003;39(9):974–7. DOI:10.1023/A:1025517507623. 13. Vanderah TA, Siegrist T, Lufaso MW, Yeager MC, Roth RS, Nino JC, Yates S. Phase formation and properties in the system Bi2O3: 2CoO1+x:Nb2O5. Eur J Inorg Chem. 2006;23:4908–14. DOI:10.1002/ejic.200600661. 14. Nguyen HB, Norẻn L, Liu Y, Withers RL, Wei X, Elcombe MM. The disordered structures and low temperature dielectric relaxation properties of two misplaced- displacive cubic pyrochlores found in the Bi2O3–M IIO–Nb2O5 (M = Mg, Ni) systems. J Solid State Chem. 2007;180:2558–65. DOI:10.1016/j.jssc.2007.07.003. 240 15. Nguyen B, Liu Y, Withers RL. The local crystal chemistry and dielectric properties of the cubic pyrochlore phase in the Bi2O3–M 2+O–Nb2O5 (M 2+ – Ni2+ and Mg2+) sys- tems. J Solid State Chem. 2007;180:549–57. DOI:10.1016/j.jssc.2006.10.039. 16. Li LX, Zhang S, Lv XS. Crystal chemistry and dielectric properties of (Bi1.5Zn0.4M0.1) (Nb1.5Zn0.5)O7 (M = Sr, Ca, Mn, Zn) pyrochlore oxides. J Mater Sci: Mater Electron. 2017;28(5):4388-95. DOI:10.1007/s10854-016-6066-0. 17. Shihua D, Yong P, Tianxiu S, Hongni W, Peng X, Lihua Y. Dielectric Properties of Ca Doping a-BZN Ceramics. Ferroelectrics. 2015;487:161–7. DOI:10.1080/0015019 3.2015.1071628 18. Luo W, Li L, Guo Q, Lv X. Crystal structure and dielectric properties of Mn-sub- stituted Bi1.5Zn1.0Nb1.5O7 pyrochlore ceramics as temperature stable LTCC material. J Mater Sci: Mater Electron. 2017;28:5623–7. DOI:10.1007/s10854-016-6232-4. 19. Du H, Shi X, Cui Y. Defect structure and electrical conduction behavior of Bi-based pyrochlores. Solid State Commun. 2010;150:1213–6. DOI:10.1016/j.ssc.2010.04.008. 20. Osman RAM, West AR. Electrical characterization and equivalent circuit analysis of (Bi1.5Zn0.5)(Nb0.5Ti1.5)O7 Pyrochlore, a relaxor ceramic. J Appl Phys. 2011;109:074106- 1-074106-8. DOI:10.1063/1.3553883. 21. Valant M, Davies PK. Crystal Chemistry and Dielectric Properties of Chemically Substituted (Bi1.5Zn1.0Nb1.5)O7 and Bi2(Zn2/3Nb4/3)O7 Pyrochlores. J Am Ceram Soc. 2000;83(1):147–53. DOI:10.1111/j.1151-2916.2000.tb01163.x. 22. Du H, Yao X, Wang H. Dielectric properties of pyrochlore (Bi1.5Zn0.5)(Nb0.5M1.5)O7 (M = Ti, Sn, Zr, and Ce) dielectrics. Appl Phys Lett. 2006;88:212901-1-212901-3. DOI:10.1063/1.2200480. 23. Qasrawi AF, Mergen A. Structural, electrical and dielectric properties of Bi1.5Zn0.92Nb1.5−xTaxO6.92 pyrochlore ceramics. Ceramics International. 2012;38:581–7. DOI:10.1016/j.ceramint.2011.07.046. 24. Wang H, Zhang D, Wang X, Yao X. Effect of La2O3 Substitution on Structure and Di- electric Properties of Bi2O3–ZnO–Nb2O5-based Pyrochlore Ceramics. J Mater Res. 1999;14(2):546–8. DOI:10.1557/JMR.1999.0078. 25. Dasin NAM, Tan KB, Khaw CC, Zainal Z, Chen SK. Subsolidus solution and electri- cal properties of Sr-substituted bismuth magnesium niobate pyrochlores. Ceramics International. 2017;43:10183–91. DOI:10.1016/j.ceramint.2017.05.043. 26. Huang B, Liu Y, Lu Y, Gao H, Chen H. Structure and dielectric properties of Nd substituted Bi1.5MgNb1.5O7 ceramics. J Mater Sci: Mater Electron. 2013;24:2785–9. DOI:10.1007/s10854-013-1171-9. 27. Ning P-F, Li L-X, Xia W-S, Zhang X-Y. Low temperature crystallized voltage tunable Bi1.5CuxMg1-xNb1.5O7 thin films capable of integration with Au electrode. Ceramics International. 2012;38:5299–303. DOI:10.1016/j.ceramint.2012.02.088. 28. Koroleva MS, Piir IV, Sekushin NA. Mg-Ni and Mg-Cu containing bismuth nio- bates: synthesis, structure and electrical properties. In: Articles of the 21h Interna- tional Conference Solid State Ionics; 2017 June 18-23; Padua, Italy. p. 357. 29. Koroleva MS, Piir IV, Sekushin NA, Istomina EI. Sintez i elektricheskie svoystva magniy-med’-, magniy-nikel’soderzhashchikh niobatov vismuta [Synthesis and electrical properties of magnesium-copper, magnesium-nickel-containing bismuth 241 niobates]. In: Articles of the First International Conference on Intellect-intensive technologies in power engineering (physical chemistry and electrochemistry of molten and solid state electrolytes); 2017 Sep 18-22; Ekaterinburg, Russia. Р. 363– 365. Russian. 30. Withers RL, Welberry TR, Larsson A-K, Liu Y, Norén L, Rundlöf H, Brink FJ. Local crystal chemistry, induced strain and short range order in the cubic pyro- chlore (Bi1.5− αZn0.5−β)(Zn0.5−γNb1.5−δ)O(7−1.5α−β−γ−2.5δ) (BZN). J Solid State Chem. 2004;177(1):231–44. DOI:10.1016/j.jssc.2003.07.005 31. Piir IV, Koroleva MS, Ryabkov YuI, Pikalova EYu, Nekipelov SV, Sivkov VN, Vyalikh DV. Chemistry, structure and properties of bismuth copper titanate pyrochlores. Solid State Ionics. 2014;262:630–5. DOI:10.1016/j.ssi.2013.08.041. 32. Krasnov AG, Piir IV, Koroleva MS, Sekushin NA, Ryabkov YI, Piskaykina MM, Sad- ykov VA, Sadovskaya EM, Pelipenko VV, Eremeev NF. The conductivity and ionic transport of doped bismuth titanate pyrochlore Bi1.6МxTi2O7−δ (М – Mg, Sc, Cu). Solid State Ionics. 2017;302:118–25. DOI:10.1016/j.ssi.2016.12.019. 33. Rodríguez-Carvajal J. Recent advances inmagnetic structure determination by neu- tron powder diffraction. Phys B Condens Matter. 1993;192:55–69. DOI:10.1016/0921- 4526(93)90108-I. 34. Shannon RD. Revised effective ionic radii and systematic studies of interatomic dis- tances in halides and chalcogenides. Acta Cryst. 1976;A32:751–67. DOI:10.1107/ S0567739476001551. 35. Allred AL, Rochow EG. A scale of electronegativity based on electrostatic force. J In- org Nucl Chem. 1958;5(4):264–8. DOI:10.1016/0022-1902(58)80003-2. 36. Singh J, Krupanidhi SB. Probing disorder in cubic pyrochlore Bi1.5Zn1.0Nb1.5O7 (BZN) thin films. Solid State Commun. 2010;150:2257–61. DOI:10.1016/j.ssc.2010.09.030. 37. Tan PY, Tan KB, Khaw CC, Zainal Z, Chen SK, Chon MP. Structural and electri- cal properties of bismuth magnesium tantalate pyrochlores. Ceramics International. 2012;38(7):5401-9. DOI:10.1016/j.ceramint.2012.03.050. 38. Tan KB, Khaw CC, Lee CK, Zainal Z, Tan YP, Shaari H. High temperature impedance spectroscopy study of non-stoichiometric bismuth zinc niobate pyrochlore. Mater Sci Pol. 2009;27:947–59. Available from: http://www.materialsscience.pwr.wroc.pl/ Cite this article as: Koroleva MS, Piir IV, Istomina EI. Synthesis, structure and electrical properties of Mg-, Ni-codoped bismuth niobates. Chimica Techno Acta. 2017;4(4):231–41. DOI:10.15826/ chimtech/2017.4.4.04.