ИСТИНА

Bi2O3-based compounds attract attention as materials with high anionic conductivity. The greatest interest is the high temperature cubic phase of Bi2O3, which has extremely high oxygen conductivity close to 3 S/cm [1]. At room temperature this phase may be stabilized by partial substitution bismuth with niobium, tantalum, calcium and rare earth elements. In a series of articles codoping bismuth with tungsten and rare earth was also studied and their conductivity reaches 0.05-1 S/cm at 500-800 ºC [2-4]. Codoping with rare earth and molybdenum, which is similar to tungsten crystallochemically, has not been studied. The purpose of this work - the synthesis of compounds in Ln2MoO6-Bi2O3 (Ln = Pr, Nd) system and study of their electrical properties. Polycrystalline samples in Ln2MoO6-Bi2O3 (Ln = Pr, Nd) systems with composition (1–x)Ln2O3+(1–x)MoO3+xBi2O3 were obtained by solid state synthesis in air. Maximum firing temperature was 800-1100 °С depending on sample compositions. Investigation shows, that solid solutions isostructural with cubic fluorite Bi2O3 phase are formed in wide area of bismuth concentrations: 0.6<x<0.9 both for Ln = Nd and Pr. The samples with less bismuth concentration (0.5<x<0.6) have tetragonal structure resulted from distortion of cubic fluorite Bi2O3 structure. Cell parameters a and c of these tetragonal compounds close to that of cubic solid solutions. The samples with x<0.5 were a mixture of two tetragonal phases based on Ln2MoO6 and Bi2O3 compounds. An intensive diffuse peak is observed on dielectric permittivity temperature dependence for all samples with cubic and tetragonal structure. The peak moves into low temperatures with decrease of bismuth concentration, from 770-800 °С (x=0.5) to 570 °С (x=0.85). The nature of this peak is not clear. The samples with tetragonal and cubic structure demonstrate high conductivity, which, analogously Bi2O3, may be caused by the diffusion of oxygen anions. For the tetragonal samples with (0.5<x<0.6) the conductivity is weakly dependent on bismuth content and reaches 0.05 S/cm at 800 °С. For cubic samples with increasing of bismuth concentration the conductivity grows on an order of magnitude. Samples with x=0.85 demonstrate the conductivity close to 0.2 S/cm at 800 °С, which is comparable with the results of [2-5]. Conductivity temperature dependences for all measured samples may be approximated by Arrhenius law with activation energy near 0.8 eV. This work was supported by Russian Foundation for Basic Research (project No. 15-02-03492). References [1] V.V. Kharton, E.N. Naumovich, A.A. Yaremchenko, F.M.B. Marques. J. Solid State Electrochem. 5 (2001) 160-187; [2] N. Jiang, E.D. Wachsman, Su-Ho Jung. Solid State Ionics. 150 (2002) 347-353; [3] A. Borowska-Centkowska, F. Krok, I. Abrahams, W. Wrobel. Solid State Ionics. 203 (2011) 22-28; [4] A. Watanabe, M. Sekita. Solid State Ionics. 176 (2005) 2429-2433. [5] T. Takahashi, H. Iwahara. J. Appl. Electrochem. 3 (1973) 65-72.