Compounds with apatite structure having the composition M10(ZO4)6X2 (where M = Na+ , K+ , Ca2+, Sr2+, Ba2+, Pb2+ , Cd2+, Y3+, La3+, REE etc.; Z = Si4+, Ge4+, P5+, V5+ , As5+, S6+, Cr6+ etc.; X = OH– , F– , Cl– , Br– , I– , O2– , (vacancies) are characterized by various properties. As a result, they are intensively studied and may be used as bioactive, luminescent and laser materials, sensors, solid electrolytes, sorbents, catalysts. In crystal chemistry the apatite formula can be represented as [M(1)]4[M(2)]6(ZO4)6X2. M(1) (4f position) is surrounded by nine oxygen atoms, which are the part of ZО4 tetrahedra. M(2) (6h position) is surrounded by six oxygen atoms being the part of ZО4 tetrahedra and X atom (position 2a) located in the structure channel. Cations in the position M(2) form triangles, their central axis coinciding with axis c. Repeating of this structure along axis c enables the formation of channels, in which X ions can be located and move. Such structure allows to make isomorphous substitution by different atoms in structural units M, Z, and X. The present study represents the results of isomorphous substitution of lead by REE of yttrium subgroup, which was mainly realized in the system Pb(8−x)TbxNa2 (PO4)6(2−x/2)O(x/2).Substitution of rare-earth elements (REEs, Ln: Tb, Dy, Ho, Tm, and Yb) for lead in the lacunary apatite Pb(8−x)LnxNa2 (PO4)6(2−x/2)O(x/2) (0 ≤ x ≤ 2) in accordance to scheme 2 Pb2+ +  → 2 Ln3+ + O2– has been studied by Xray powder diffraction (including the Rietveld refinement), scanning electron microscopy and FT-IR spectroscopy. Single phase solid solutions Pb(8−x)LnxNa2 (PO4)6(2−x/2)O(x/2) are formed in the range from х = 0.00 to х = 0.55. By changing the parameters of elementary cells from the composition and the phase-vanishing method the solubility limits xmax of REE decreases with an REE atomic number increasing from 0.55 till 0.12 at 800 °C (xmax = 0.53–0.55 for Tb, xmax = 0.45 for Dy, xmax = 0.38 for Ho, xmax = 0.16–0.18 for Tm, and xmax = 0.12 for Yb) were established. Refinements of X-ray diffraction patterns by the Rietveld method show that substitution lead to Pb(2)—O(1,2,3) and Pb(2)—O(2) atomic distances decreases. This study shows that REE atoms substitute for Pb preferentially at the Pb(2) sites of the apatite structure.

Sodium neodymium silicate NaNd 9 (SiO 4 ) 6 O 2 with the apatite structure has been synthesized and studied by X-ray diffraction and scanning electron microscopy. No sodium oxide sublimation occurred during ceramic synthesis by the selected method. The Rietveld method shows that sodium atoms in the structure are ordered (in the 4 f position). The O(4) oxygen atoms, which are not involved in silicate ions, are positioned in the centers of triangles formed by Nd(2) atoms. Rather long Nd-Nd distances (3.940 Å) indicate a possible existence of luminescent properties.

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.

Substitution of samarium for strontium in hydroxyapatite corresponded to the scheme Sr2+ + OH- -> Sm3+ + O2- has been investigated by X-ray powder diffraction and IR spectroscopy. It was established that solid solutions Sr10-xSmx (PO4)(6)(OH)(2-x)O-x are formed in the range of x = 0-1.6 at 1100 degrees C in air. Crystal features of some samples have been refined by Rietveld method. It was shown that Sm3+ preferably occupy the Sr(2) site. The hydroxyapatite dehydration occurring under the scheme 2OH(-) -> O2- + square was confirmed by IR spectra of obtained samples.

Isomorphous substitution of samarium and gadolinium for calcium in synthetic hydroxyapatite by the scheme Ca2+ + OH− → Ln3+ + O2− was studied by X-ray powder diffraction and IR spectroscopy. The homogeneity region of Ca10 − x Ln x (PO4)6(OH)2 − x O x phases of variable compositions synthesized at 1100°C was found to exist up to x of 1.8 for Sm and 1.4 for Gd. In the heterogeneous region of solid solutions, phases with Ln3PO7 and LnPO4 structures were formed. The structures of some solid solutions were refined by the Rietveld method, which allowed us to establish that the substitution of Ln3+ ions for Ca(2) positions is preferred. Changes in the intensities of the absorption bands of stretching and libration vibrations of OH groups are indicative of a partial dehydration of oxyhydroxyapatite. The substitution was shown to decrease Ca(2)-O(OH) and P-O distances and increase Ca(2)-O(1,2,3) distances.

The CaO-3 (1 + x)CuO-4TiO2 system was studied using powder X-ray diffraction in the concentration region near calcium copper titanate. A single-phase material is formed in this system only when x ∼ 0. An excess or deficit of copper gives rise to extra phases: CuO or CaTiO3 and TiO2, respectively. Impurities increase the dielectric constant of CaCu3Ti4O12-based ceramics. An excess of copper oxide (x ∼ 0.08) increases ɛ more than tenfold.

We have studied the effect of bismuth oxide additions (2 wt %) on the electrical properties of thick lead zirconate titanate films. The results demonstrate that the addition of bismuth oxide to the starting mixture, followed by grinding in a high-energy vibratory mill, enables the sintering temperature to be lowered to 820–850°C.

Isomorphic substitution of neodymium and gadolinium for calcium in synthetic hydroxovanadate Ca 5 − x M x (VO 4 ) 3 (OH) 1 − x O x (M = Nd, Gd) is studied in the range 700–1000°C using X-ray powder diffraction, single-crystal X-ray diffraction (Rietveld technique), and IR spectroscopy. Single-phase solid solutions at 800°C are formed with x ≤ 0.35 for M(III) = Nd and x ≤ 0.3 for M(III) = Gd. With high x , the apatite solid solution coexists with Ca 3 (VO 4 ) 2 , Nd 2 O 3 , and X phases. With increasing x in the homogeneous region, the intensity of the bands of stretching vibrations and librations of OH groups decrease. Single-crystal X-ray diffraction shows that neodymium and gadolinium substitute for calcium in solid solutions mostly in Ca(2) positions.

A possibility of substitution of barium for strontium in Sr10(VO4)6(OH)2 is studied by X-ray powder diffraction and IR spectroscopy. According to X-ray powder diffraction data, single-phase solid solutions Sr10 − x Ba x (VO4)6(OH)2 are formed with x = 0–2.5 with an increase in the unit cell parameters.

Using the X-ray phase analysis and IR spectroscopy, the isomorphic substitution of samarium for strontium according to the Sr2++OH--> Sm3++O2- has been studied in a synthetic hydroxyapatite corresponding to the system composition Sr5-xSmx(VO4)(3)(OH)(1-x)O-x (0 <= x <=.40). The solid solutions on the basis of strontium hydroxyapatites (synthesized at 800 degrees C from solutions) have been established to be formed within limits 0<x<0.12. The crystal structure of the solid solutions obtained has been refined by the Rietveld method.

Neodymium-for-strontium isomorphic substitutions in synthetic hydroxovanadate Sr5 − x Nd x (VO4)3(OH)1 − x O x were studied from 600 to 800°C using powder and single-crystal X-ray diffraction (the Rietveld technique) and IR spectroscopy. Single-phase solid solutions at 800°C are formed in the range up to x = 0.14. At higher x, a Sr3(VO4)2 phase exists along with the apatite solid solution. In the range of 0 < x ≤ 0.14, the intensity of the IR bands due to the stretching and libration vibrations of OH groups decreases with increasing x. Single-crystal X-ray diffraction shows that neodymium mostly substitutes for strontium atoms at the Sr(1) sites in the solid solution with x = 0.14.

Using X-ray phase analysis, the calcium substitution with Nd and Dy in hydroxyapatite Ca(10-x)Ln(x)(PO4)(2-x)O-x at 1100 degrees C has been established to take place up to x = 2.0 and 1.4, respectively. The IR spectroscopy has shown that along with the Ca2+ + OH- -> Ln(3+) + O2- substitution, the 2OH(-) -> O2- + square one occurs. The structure refinement using Rietveld method has shown that Nd and Dy ions occupy mainly the Ca(2) positions. The Ca2+ + OH- -> Ln(3+) + O(2- )substitution has been established to strengthening of the Ca(2)-O(4) bond but weakens somewhat the Ca(2)-O(1,2,3) ones.