The polycrystalline samples of the x/6Pr6O11 – MoO3 (2 ≤ x ≤ 6) series were prepared by conventional solid-state route. The phase formation was studied by XRD analysis in the temperature range of 1000 – 1200°C. After calcination at 1100°С, the formation of praseodymium molybdate with Pr4MoO9+δ composition is observed, which decomposes into a mixture of Pr2MoO6 and Pr6MoO12+δ phases at 1200°С. It was first established that Pr4MoO9+δ praseodymium molybdate has a monoclinic lattice with parameters a = 16.7211(9) Å, b = 11.9894(7) Å, c = 9.5588(5) Å, β = 109.6149(7) °, sp. gr. C 2/m. Crystal structure was refined by high resolution neutron diffraction data. The homogeneity regions of Pr4MoO9+δ and Pr6MoO12+δ were determined to be 4 < x < 4.2 and 4.57 < x < 6, respectively. It was shown that the conductivity of this molybdates increases with praseodymium oxide content in the Pr5Mo3O16+δ – Pr4MoO9+δ – Pr6MoO12+δ series.

— Isomorphous bismuth substitution for neodymium in the Nd 5 Mo 3 O 16 + δ compound has been studied by X-ray diffraction. The crystal structure of a single-phase solid solution with the composition Nd 4.95 Bi 0.05 Mo 3 O 16 + δ has been refined by the Rietveld method, and the electrical conductivity of the modified molybdate has been measured in the temperature range 300–700°C.

This paper presents the investigation of the heterovalent substitution of cadmium for lanthanum in the La2-xCdxMoO6-x/2 system. The samples were synthesized by the solid state reaction method at 1000°C. The samples were characterized by X-ray powder diffraction with Rietveld refinements, scanning electron microscopy with energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy methods. The study results revealed that cadmium incorporation in the lanthanum molybdate leads to the transformation of the tetragonal structure of La2MoO6 to a cubic fluorite-like one. The content of the cubic phase reaches 94% in the Lа1.4Cd0.6MoO5.7 sample. The unit cell parameter of fluorite-like-phase decreases with cadmium content rising. The preferred location of cadmium ions in the cubic structure was established by the Rietveld refinement method. The heterovalent substitution cadmium for lanthanide in tetragonal La2MoO6 molybdate leads to the cubic fluorite phase stabilization in a similar way as it occurs in the process of reduction.

Sodium holmium double silicates with the apatite structure and compositions NaHo 9 (SiO 4 ) 6 O 2 and Na 2 Ho 8 (SiO 4 ) 6 O have been prepared by a sol-gel process and characterized by X-ray diffraction. The crystal structure of NaHo 9 (SiO 4 ) 6 O 2 has been refined, and the electrical conductivity of both compounds has been measured.

Двойные силикаты натрия и гольмия со структурой апатита состава Na2Ho8(SiO4)6O и NaHo9(SiO4)6O2 синтезированы золь–гель-методом. Соединения изучены методом рентгенофазового анализа, уточнена кристаллическая структура NaHo9(SiO4)6O2, измерены электрофизические свойства.

Substitution rare-earth elements for cadmium in the monoclinic compounds Ln2MoO6 (Ln – Gd, Ho) leads to the formation of fluorite-related cubic structure. Series Ln2xCdxMoO6x/2 was investigated by XRD (with structure refinement), scanning electron microscopy, FTIR-spectroscopy and conductivity measurements.

Samarium substitution for neodymium in the Nd 5 Mo 3 O 16 compound has been studied by X-ray diffraction, scanning electron microscopy, and IR spectroscopy. The results demonstrate that fluorite-like Nd 5– x Sm x Mo 3 O 16 solid solutions exist in the range x ≤ 2. The electrical conductivity of the solid solutions increases with increasing samarium content in the range x = 0–1. Structure refinement by the Rietveld method for Nd 4 SmMo 3 O 16 has shown that the Nd(2) coordination polyhedron in this solid solution is distorted more severely than that in the structure of Nd 5 Mo 3 O 16 .

Substitution rare-earth elements for cadmium in the monoclinic compounds Ln 2 MoO 6 (Ln – Gd, Ho) leads to the formation of fluorite-related cubic structure. Series Ln 2 x Cd x MoO 6 x/2 was investigated by XRD (with structure refinement), scanning electron microscopy, FTIR-spectroscopy and conductivity measurements.

The substitution neodymium for ytterbium in compounds Nd 5 Mo 3 O 16 was investigated by X-ray diffraction. Solid solution Nd 5-x Yb x M o3 O 16 with cubic fluorite-related structure is formed in the composition rage up to x = 0,7. The substitution limit was determined by inflection of parameter a of cubic phase and by disappearing-phase method. It is near 3 at. %. The dependence of specific conductivity on composition is non-linear and has the minimum on x = 0,05.

Substituted hydroxyapatite samples of composition Ca 10− x Pr x (PO 4 ) 6− x (SiO 4 ) x (OH) 2 , where x = 0−6, were studied using X-ray diffraction and IR spectroscopy. Calcium substitutions occurred over the entire range of compositions studied. The crystal structure of solid solutions was refined by the Rietveld technique.

As a result of our study of the influence that a deficiency and an excess of components in the solid solution of lead zirconate-titanate of composition PbTi/sub 0.1/Zr/sub 0.9/O/sub 3/, doped with manganese oxide, have on the electrophysical properties we have established that the quality of lead zirconate-titanate ceramics can be improved not only by regulating the lead oxide content, as described earlier for compositions near the morphotropic transition of a tetragonal structure to a rhombohedral structure, but by altering the concentration of titanium and zirconium oxides in the mixture.