Bogdan I. Lazoryak

Whitlockite solid solutions Ca9−x M x R(PO4)7 (x = 1, 1.5; M = Mg, Zn, Cd; R = Ln, Y) with antiferroelectric properties

Whitlockite solid solutions Ca9−xMxR(PO4)7 (M = Mg, Zn, Cd; R = Ln, Y) were synthesized as powders and ceramics using solid-phase synthesis. Dielectric investigations and second harmonic generation (SHG) tests showed that ferroelectric (FE) phase transitions existing in samples with x = 0 change to antiferro-electric (AFE) transitions between two centrosymmetrical phases in samples with x = 1 or 1.5. The calcium-ion solid electrolyte conductivity in Ca9−xMxR(PO4)7 at high temperatures appears either as a result of an antiferroelectric-paraelectric (AFE-PE) phase transition (for x = 1) or as a result of a separate phase transition near 1173 K (for x = 1.5). The appearance of dielectric properties in whitlockites is discussed with reference to the features of their polar and centrosymmetrical structures.

Triple phosphates of calcium, sodium and trivalent elements with whitlockite-like structure

Triple phosphates of calcium, sodium and trivalent elements (Eu, Nd, Fe) in Ca3(PO4)2-RPO4-Na3PO4 systems were predicted on the basis of crystal chemistry data and synthesized. The obtained phases were studied by XRD, IR-spectroscopy and emission spectroscopy under 90Sr-90Y and λ = 380 nm excitation. The only phosphates with the whitlockite-like structure appear within the range of Ca3(PO4)2-Ca9Na1.5R0.5(PO4)7-Ca10Na(PO4)7 compositi The emission spectra of phases with europium under 90Sr-90Y excitation consist of transition lines 5D0 → 7Fj in Eu3+ and two broad bands of inherent luminescence of the matrix with maximums at ~ 360 and ~ 510 nm.

Crystal structures of double calcium and alkali metal phosphates Ca10M(PO4)(7) (M = Li, Na, K)

Crystal structures of double calcium and alkali metal phosphates described by the general formula Ca10M(PO4)7(M = Li, Na, K) have been studied by the Rietveld method. The lattice parameters are a = 10.4203(1) and c = 37.389(1) Å (for M = Li), a = 10.4391(1) and c = 37.310(1) Å (for M = Na), and a = 10.4229(1) and c = 37.279(2) Å (for M = K); sp. gr. R3c, Z = 6. The specific features of the distribution of alkali metal cations over the structure positions are discussed.

The new phosphates Ca9MLn2/3(PO4)7(M= Li, Na; Ln = rare earth, Y, Bi)

Abstract The new family of triple phosphates Ca 9 MLn 2 3 (PO 4 ) 7 ( Ln = rare earth, Y, Bi; M = Li + , Na + has been synthesized and studied by X-ray powder diffraction, IR-spectroscopy, differential thermal analyses and luminescence. All compounds have the whitlockite-like structure (space group R3c). Cell parameters, IR and emission (Eu 3+ ) spectra are given. The luminescence properties of trivalent europium are analyzed in Ca 9 NaEu 2 3 (PO 4 ) 7 and Ca 9 LiEu 2 3 (PO 4 ) 7 at 290 K. The fluorescence lifetime of the 4 F 3 2 − 4 I 11 2 transition of Nd 3+ is reported for the solid solutions Ca 9 Nd x Gd 1 − x (PO 4 ) 7 , Ca 3 − x Nd 2x 3 (PO 4 ) 2 and Ca 9 M(Nd x Gd 1 − x ) 2 3 (PO 4 ) 7 (M = Li, Na).

Synthesis and crystal structure of Ca9Cu1.5(PO4)7 and reinvestigation of Ca9.5Cu(PO4)7

Abstract Ca 9 Cu 1.5 (PO 4 ) 7 was synthesized by the solid-state method at 1273 K followed by quenching in air. Crystal structure of Ca 9 Cu 1.5 (PO 4 ) 7 was refined by the Rietveld method: space group R 3c, a = 10.3379(1) A, c = 37.1898(3) A, Z = 6 with R wp = 4.87%, R p = 3.67%, S = 1.58, R I = 2.42%, R F = 1.07%. The structure of Ca 9 Cu 1.5 (PO 4 ) 7 is isotypic with β-Ca 3 (PO 4 ) 2 and Ca 9.5 Cu(PO 4 ) 7 . The M (5) site is fully occupied, and the M (4) site is half occupied by copper cations. The M (1)- M (3) sites are occupied by calcium cations. Copper cations in the M (4) site are displaced from the threefold axis due to long distances M (4)—O. Reinvestigation of crystal structure of Ca 9.5 Cu(PO 4 ) 7 showed that the M (5) site is occupied by 0.79(1)Cu 2+ + 0.21Ca 2+ , and other copper cations locate in the M (4) site.

Crystal structures of new triple Ca9CoM(PO4)7 (M = Li, Na, K) phosphates

Abstract New triple phosphates Ca9CoM(PO4)7 (M = Li, Na, K) were synthesized by solid state method. Their crystal structures were determined by Rietveld analysis. They are related to tricalcium phosphate and crystallize into trigonal system (space group R3c) with unit-cell parameters a = 10.3276(1) A, c = 37.100(1) A, M = Li; a = 10.3515(1) A, c = 37.073(1) A, M = Na; a = 10.4017(1) A, c = 37.009(1) A, M = K. All five independent cation sites are filled in Ca9CoM(PO4)7 (M = Li, Na, K). Cobalt occupies the octahedral site M(5). Alkali metal cations occupy the M(4) site.

Redox reactions in double calcium and iron phosphates

Abstract The redox reactions in Ca 9 Fe(PO 4 ) 7 and Ca 9 FeH 0.9 (PO 4 ) 7 were studied under hydrogen-containing and oxygen-containing atmosphere by XRD, DTA, TG, Mossbauer spectroscopy and magnetic measurement. The redox reactions proceed reversibly. The oxygen stoichiometry is not variable in these compounds. The redox cycle can by repeated for many times without the destruction of the crystal lattice.

Influence of alumina on the properties of continuous basalt fibers

We study the influence of alumina percentage on fundamental properties (structure and crystallization) and applied properties (temperature range of manufacturing and strength) of basalt glasses and continuous basalt fibers (CBFs) on their base. Crystallization of high-alumina glasses and CBFs occurs in three steps. First, magnetite crystallizes, serving as nuclei for subsequent crystallization of augite mineral. Above 900°C, anorthite is the major crystallization product. For low-alumina fibers, augite is the major crystallization product. Fibers and glasses having high alumina percentages have the highest resistance to crystallization. IR spectroscopy showed that the structural connectivity of glasses and fibers increases with increasing alumina percentage. The breaking strength of fibers varies within 1.7–2.5 GPa, increasing with Al2O3 percentage.

Crystal structure of double vanadates Ca9R(VO4)7. II. R = Tb, Dy, Ho, and Y

Crystal structures of the compounds Ca9R(VO4)7 (R = Tb (I), Dy (II), Ho (III), and Y (IV) have been studied by the method of the full-profile analysis. All the compounds are crystallized in the trigonal system (sp. gr. R3c, Z = 6) with the unit-cell parameters (I) a = 10.8592(1), c = 38.035(1), V = 3884.2(2) Å3; (II) a = 10.8564(1), c = 38.009(1) Å, V = 3879.6(2) Å3, (III) a = 10.8565(1) and c = 37.995(1) Å, V = 3878.3(2) Å3, and (IV) a = 10.8588(1), c = 37.995(1) Å, V = 3879.9(2) Å3. In structures I–IV, rare earth and calcium cations occupy three positions—M(1), M(2), and M(5). Rare earth cations occupy the R3+ positions almost in the same way: 2.7–2.6(2) cations in the M(1) position; 2.7–2.3(2) cations in the M(2) position, and 0.6–1.0(1) cation in the M(5) position. At the same time, the occupancy of the M(5) position regularly increases with a decrease of the R3+ radius.

Large second order optical nonlinearity in thermally poled amorphous niobium borophosphate films

Thin films of sodium niobium borophosphate glass were deposited on silicon wafer and borosilicate glass substrates by radio frequency sputtering. Thermal poling of the films was performed under various voltage conditions. The chemical composition of the films after poling was controlled by x-ray energy dispersive spectroscopy and compared to the initial composition. The second harmonic signals generated by thermal poling were analyzed in reflection mode. The recorded complex Maker fringes pattern signals were simulated and fitted using a multilayer model for the estimation of the second harmonic generation nonlinear coefficients χ(2). The results are compared to previously published χ(2) coefficients obtained for bulk oxide glasses (∼3pm∕V, approximately fourfold as strong as the highest value reported in thermally poled fused silica). Resulting from this study thermally poled niobium sodium borophosphate thin films are revealed of real interest as potential electro-optic devices.