Interactions in ternary bismuth-containing molybdate systems M2MoO4-Bi2(MoO4)3-Zr(MoO4)2 in the subsolidus region

A fundamental problem in materials science consists in establishing a relationship between the chemical composition, structure, and properties of materials. This issue can be solved through the study of multicomponent systems and the directed synthesis of promising compounds. Of practical interest here are active dielectrics that are based on complex oxide compounds, specifically molybdates. Among complex molybdates and tungstates, ternary caged molybdates of the following structural types are of greatest importance: nasicon, perovskite, langbeinite, etc. Due to their widely varying elemental and quantitative compositions, such molybdates are convenient models for structural and chemical design, as well as the establishment of “composition–structure– properties” genetic relationships. Bismuth-containing complex molybdate systems exhibit the formation of phases having ferro-piezoelectric, ionic, and other properties. In this work, the Rb2MoO4–Bi2(MoO4)3–Zr(MoO4)2 ter nary salt system was studied for the first time using the method of intersecting sections in the subsolidus region (450–650 ℃). To this end, quasibinary sections were identified; triangulation was performed. Ternary molybdates Rb5BiZr(MoO4)6 and Rb2BiZr2(MoO4)6,5 were formed in the system using a ceramic technology. These compounds are isostructural to the previously obtained REE molybdates (M5LnZr(MoO4)6) but contain trivalent bismuth instead of rare earth elements. The structure of Rb5BiZr(MoO4)6 was adjusted via the Rietveld refinement technique using the TOPAS 4.2 software package. The ternary molybdate crystallizes in a trigonal system, with the following unit cell parameters of the R`3c space group: a = 10.7756(2) and c = 39.0464(7) Å. According to the studies of thermal properties exhibited by M5BiZr(MoO4)6, these ternary molybdates undergo the first-order phase transition in the temperature range of 450–600 ºC. The IR and Raman spectra of M5BiZr(MoO4)6 reveal the crystallization of ternary molybdates in the R`3c space group. The conducted comparative characterization of M2MoO4–Bi2(MoO4)3–Zr(MoO4)2 phase diagrams suggests that the phase equilibria of these systems depend on the nature of molybdates of monovalent elements.

Phase formation in the Ag2MoO4–Rb2MoO4–Hf(MoO4)2 system

Systematic studies of the subsolidus structure of ternary molybdate systems allow expanding the representation of ternary molybdates. In this paper we studied the solid phase interaction in the Ag2MoO4–Rb2MoO4–Hf(MoO4)2 system for the first time using X-ray phase analysis.To determine the quasi-binary sections, we use the method of “intersecting cuts”. It helped to reveal the formation of new Rb5Ag1/3Hf5/3(MoO4)6 and Rb3AgHf2(MoO4)6 phases. We also determined their thermal characteristics using differential scanning calorimetry. The ternary molybdate Rb5Ag1/3Hf5/3(MoO4)6 crystallised in the trigonal syngony with the followingunit cell parameters: a = 10.7117(1), c = 38.5464(5) Å (space group R3с, Z = 6). The Ag2MoO4–Rb2MoO4–Hf(MoO4)2 system is characterised by the existence of ten quasi-binary cross sections.The experimental data obtained in this work complement the information on phase equilibria in condensed ternary systems containing molybdates of tetravalent elements and two different monovalent elements. This provides opportunities for the combination of the compositions of ternary molybdates due to cationic substitutions, which will allow controlling their properties.

New compounds Li3Ba2Bi3(XO4)8 (X = Mo, W): synthesis and properties

New compounds Li3Ba2Bi3(XO4)8(Х = Mo, W) were obtained by the ceramic technology. Those are the first representatives of the ternary molybdates and tungstates Li3Ba2Bi3(XO4)8 family, which contain different from the rare earth elements trivalent metal. The sequence of chemical transformations occurring during the Li3Ba2Bi3(WO4)8 formation has been established. The primary characterization of the obtained phases was carried out and their ion-conducting properties were studied. The synthesized compounds are shown to melt incongruently, isostructural to the lanthanide-containing analogues (structural type of BaNd2(MoO4)4, sp. gr. C2/c) and crystallize in the monoclinic crystal system with unit cell parameters а = 5.2798(1), b = 12.8976(4), c = 19.2272(5) Å, β = 90.978(2)° (Х = Mo), а = 5.2733(2), b = 12.9032(4), c = 19.2650(6) Å, β = 91.512(3)° (Х = W). Li3Ba2Bi3(XO4)8 are found to undergo the diffuse first-order phase transitions at 441°C (molybdate) and 527°C (tungstate), after that their conductivity reaches values of 10–3–10–4 S/cm.