K. N. Fedorov

Phase formation in the Rb2MoO4-Er2(MoO4)3-Hf(MoO4)2 system and the crystal structure of new triple molybdate Rb5ErHf(MoO4)6

AbstractThe subsolidus region of the Rb2MoO4-Er2(MoO4)3-Hf(MoO4)2 ternary salt system is studied using X-ray powder diffraction. A novel 5: 1: 2 triple molybdate, Rb5ErHf(MoO4)6, is found to form in the system. Crystals of Rb5ErHf(MoO4)6 are flux-grown under spontaneous nucleation conditions. The composition and crystal structure of Rb5ErHf(MoO4)6 are refined in a single-crystal X-ray diffraction experiment (X8 APEX diffractometer, MoKα radiation, 1753 reflections, R = 0.0183). The crystals are trigonal; a = 10.7511(1) Å, c = 38.6543(7) Å, V = 3869.31(9) Å3, dcalc = 4.462 g/cm3, Z = 6, space group % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaamOuaiqaio% dagaqeaiaadogaaaa!3881!

Phase equilibria in the systems Rb2MoO4-R2(MoO4)3-Hf(MoO4)2 (R = Al, In, Sc, Fe(III)) and the crystal structure of double molybdate RbFe(MoO4)2

R\bar 3c

Phase equilibria in the Tl2MoO4-Nd2(MoO4)3-Hf(MoO4)2 system and the crystal structure of double molybdate TlNd(MoO4)2

. The mixed three-dimensional framework of the structure is formed of MoO4 tetrahedra, each sharing corners with two ErO6 and HfO6 octahedra. Two types of Rb atoms occupy large cavities of the framework. The distribution of the Er3+ and Hf4+ cation over two positions is refined in the course of structure solution.

Synthesis of ternary potassium, magnesium, and zirconium molybdates. The crystal structure of K5(Mg0.5Zr1.5)·(MoO4)6

Triple molybdates of the compositions Rb5LnHf(MoO4)6 (5:1:2) and Rb2LnHf2(MoO4)6.5 (2:1:4), Ln = Ce-Lu, were prepared by solid-phase reactions. The temperature dependence of the electrical conductivity of the compounds Rb5LnHf(MoO4)6 (5:1:2) at 200–500°C was studied.

Systems Tl2MoO4-E(MoO4)2, where E = Zr or Hf, and the crystal structure of Tl8Hf(MoO4)6

The systems Rb2MoO4-R2(MoO4)3-Hf(MoO4)2 have been investigated in the subsolidus region by X-ray powder diffraction, DTA, and IR spectroscopy. Triple molybdates of the composition 5: 1: 2 are formed in the systems with R = Al, In, Sc, and Fe. Molybdates of composition 5: 1: 3 and 1: 1: 1 are found in the iron(III)-containing system in addition to the 5: 1: 2 molybdate. Single crystals of the double molybdate RbFe(MoO4)2, which is formed in the Rb2MoO4-Fe2(MoO4)3 system, have been grown. The structure of this double molybdate has been refined using X-ray diffraction data (X8 APEX automated diffractometer, MoKα radiation, 373 F(hkl), R = 0.0287). The trigonal unit cell parameters are the following: a = b = 5.6655(2) Å, c = 7.5061(4) Å, V = 208.65(1) Å3, Z = 1, ρcalc = 3.670 g/cm3, space group R3m1. The structure is formed by layers of FeO6 octahedra sharing corners with MoO4 tetrahedra and RbO12 icosahedra.

Subsolidus phase equilibrium in Cs2MoO4-Al2(MoO4)3-Zr(MoO4)2 system and crystal structure of new ternary molybdate Cs(AlZr0.5)(MoO4)3

The possibility of ternary molybdates of compositions Tl5LnHf(MoO4)6 (5 : 1 : 2) (Ln = Dy-Lu), TlLnHf0.5(MoO4)3 (1 : 1 : 1) (Ln = Ce-Nd), and Tl2LnHf2(MoO4)6.5 (2 : 1 : 4) (Ln = Dy-Lu) was investigated by a method of solid state reactions. A temperature dependence of electrical conductivity in the temperature range 200–500°C was studied.

Growth and crystal structure of binary molybdate CsFe(MoO4)2

The Tl2MoO4-Nd2(MoO4)3-Hf(MoO4)2 system was studied in the subsolidus region using X-ray powder diffraction. New triple molybdates were found to exist in this system: Tl5NdHf(MoO4)6 (5: 1: 2), TlNdHf0.5(MoO4)3 (1: 1: 1), and Tl2NdHf2(MoO4)6.5 (2: 1: 4). The first TlNd(MoO4)2 single crystals were grown from melt solutions with spontaneous nucleation. Their crystal structure was refined from X-ray diffraction data (Bruker X8 Apex automated diffractometer, MoKα radiation, 386 F(hkl), R = 0.0136). The tetragonal unit cell parameters are as follows: a = 6.3000(2) Å, c = 9.5188(5) Å, V = 377.80(3) Å3, Z = 2, ρcalcd = 5.876 g/cm3, space group P4/nnc. The structure is a framework built of NdO8 and TlO8 tetragonal antiprisms linked via shared lateral edges and alternating in the checkerboard order. Layers share oxygen vertices with MoO4 interlayer tetrahedra and are linked into the framework.

Subsolidus phase diagrams of the systems Cs2MoO4-R2(MoO4)3-Zr(MoO4)2, where R = Al, Sc, or In

Three (5∶1∶3, 1∶1∶1, and 2∶1∶6) ternary phases were discovered in the K2MoO4−AMoO4−Zr(MoO4)2 system, where A is Mg or Mn. For A=Mg, we have synthesized 5∶1∶3 single crystals and determined their crystal structure from X-ray diffraction data (a CAD-4 automatic diffractometer, MoKα radiation, 1166 F(hkl), and R=0.026). The compound crystallizes in the trigonal system with space group R3c, a=10.576(1), c=37.511(3), Å, Z=6, dcalc=3.576, and dmsd=3.54 g/cm3. The structure is a three-dimensional composite framework of alternating Mo tetrahedra and (Mg, Zr) octahedra, which are linked via the common O vertices. Potassium atoms of three kinds are located in large framework cavities. Their polyhedra (ten-vertex polyhedra and a cubeoctahedron) are linked together by common faces and edges to form infinite zigzag columns of a large section. When solving the structure, we refined the composition of the crystals and the distribution of Mg2+ and Zr4+ cations in the M(1) and M(2) positions resulting in the formula above.