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Single crystals of the langbeinite-type phosphates K1.65Na0.35TiFe(PO4)3 and K0.97Na1.03Ti1.26Fe0.74(PO4)3 were grown by crystallization from high-temperature self-fluxes in the system Na2O–K2O–P2O5–TiO2–Fe2O3 using fixed molar ratios of (Na+K):P = 1.0, Ti:P = 0.20 and Na:K = 1.0 or 2.0 over the temperature range 1273–953 K. The three-dimensional framework of the two isotypic phosphates are built up from [(Ti/Fe)2(PO4)3] structure units containing two mixed [(Ti/Fe)O6] octa­hedra (site symmetry 3) connected via three bridging PO4 tetra­hedra. The potassium and sodium cations share two different sites in the structure that are located in the cavities of the framework. One of these sites has nine and the other twelve surrounding O atoms. [ABSTRACT FROM AUTHOR]

Cubic crystals of tripotassium aluminium (or gallium) nitridotriphosphate, K3MIII(PO3)3N (MIII = Al, Ga), were grown by application of the self-flux method. In their isostructural crystal structures, all metal cations and the N atom occupy special positions with site symmetry 3, while the P and O atoms are situated in general positions. The three-dimensional framework of these oxidonitridophosphates is built up from [MIIIO6] octa­hedra linked together via (PO3)3N groups. The latter are formed from three PO3N tetra­hedra sharing a common N atom. The coordination environments of the three potassium cations are represented by two types of polyhedra, viz. KO9 for one and KO9N for the other two cations. An unusual tetra­dentate type of coordination for the latter potassium cations by the (PO3)3N6– anion is observed. These K3MIII(PO3)3N (MIII = Al, Ga) compounds are isostructural with the Na3MIII(PO3)3N (MIII = Al, V, Ti) compounds. [ABSTRACT FROM AUTHOR]

Polycrystalline potassium nickel(II) hafnium(IV) tris(orthophosphate), a langbeinite-type phosphate, was synthesized by a solid-state method and refers to langbeinite-type phosphates. The three-dimensional framework of the title compound is built up from two types of [MO6] octahedra [the M sites are occupied by Hf:Ni in ratios of 0.754 (8):0.246 (8) and 0.746 (8):0.254 (8), respectively] and [PO4] tetrahedra are connected via O vertices. The K+ cations are located in two positions within large cavities of the framework, having coordination numbers of 9 and 12. The Hf, Ni and K sites lie on threefold rotation axes, while the P and O atoms are situated in general positions. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of TiN with Na2O–K2O–P2O5 melts was investigated at (Na+K)/P molar ratios of 0.9, 1.0, and 1.2 and at Na/K molar ratios of 1.0 and 2.0. Interactions in the system led to the loss of nitrogen and the partial loss of phosphorus and resulted in the formation of KTiP2O7 and langbeinite‐type K2−xNaxTi2(PO4)3 (x=0.22–0.26) solid solutions over the temperature range of 1173 to 1053 K. The phase compositions of the obtained samples were determined by using X‐ray diffraction (including Rietveld refinement), scanning electron microscopy (using energy‐dispersive X‐ray spectroscopy and element mapping), FTIR spectroscopy, and thermogravimetric analysis/differential thermal analysis. K1.75Na0.25Ti2(PO4)3 was characterized by single‐crystal X‐ray diffraction [P213 space group, a=9.851(5) Å]. The 3D framework is built up by TiO6 octahedra and PO4 tetrahedra sharing all the oxygen vertices with the formation of cavities occupied by K(Na) cations. Only one of the two crystallographically inequivalent potassium sites is partially substituted by sodium, and this was confirmed by calculating the bond‐valence sum. The thermodynamic stability of K1.75Na0.25Ti2(PO4)3 crystals and the preferable occupation sites of NaK cationic substitutions were investigated by DFT‐based electronic structure calculations performed by the plane‐wave pseudopotential method. [ABSTRACT FROM AUTHOR]

Abstract: The interaction of TiN with Na2O–K2O–P2O5 melts was investigated at (Na+K)/P molar ratios of 0.9, 1.0, and 1.2 and at Na/K molar ratios of 1.0 and 2.0. Interactions in the system led to the loss of nitrogen and the partial loss of phosphorus and resulted in the formation of KTiP2O7 and langbeinite‐type K2−xNaxTi2(PO4)3 (x=0.22–0.26) solid solutions over the temperature range of 1173 to 1053 K. The phase compositions of the obtained samples were determined by using X‐ray diffraction (including Rietveld refinement), scanning electron microscopy (using energy‐dispersive X‐ray spectroscopy and element mapping), FTIR spectroscopy, and thermogravimetric analysis/differential thermal analysis. K1.75Na0.25Ti2(PO4)3 was characterized by single‐crystal X‐ray diffraction [P213 space group, a=9.851(5) Å]. The 3D framework is built up by TiO6 octahedra and PO4 tetrahedra sharing all the oxygen vertices with the formation of cavities occupied by K(Na) cations. Only one of the two crystallographically inequivalent potassium sites is partially substituted by sodium, and this was confirmed by calculating the bond‐valence sum. The thermodynamic stability of K1.75Na0.25Ti2(PO4)3 crystals and the preferable occupation sites of NaK cationic substitutions were investigated by DFT‐based electronic structure calculations performed by the plane‐wave pseudopotential method. [ABSTRACT FROM AUTHOR]

Herein, the peculiarities of complex phosphate formation in self-fluxes of Cs–MII–Bi–P–O (MII = Ca, Sr, Ba and Pb) systems with Cs/P = 0.7–1.3 at fixed ratios of Bi/P = 0.2 and Bi/MII = 1.0 were studied and discussed. Three novel isostructural diphosphates with the general composition Cs3MIIBi(P2O7)2 (MII = Ca, Sr and Pb) and the original framework topology were synthesized and characterized via single-crystal and powder X-ray diffraction, SEM, DTA, and FTIR- and UV-VIS-spectroscopy. In addition, electronic structure (DFT) and Voronoi–Dirichlet polyhedra (VDP) characteristics calculations and crystallochemical analysis were performed. In the structure of the new compounds, the MIIO7 and BiO6 polyhedra are connected via common oxygen vertices forming infinite helical-like chains, which are linked by P2O7 groups into a 3D-framework with pentagonal tunnels, where the Cs+ cations are located. The structural peculiarities are discussed considering perspectives for the creation of new luminescent materials. The dielectric bandgaps, Eg, of the Cs3MIIBi(P2O7)2 crystals reveal an ∼0.2 eV low-energy shift in the Ca–Sr–Pb sequence of MII cations, which reveals the possibility to tune the optical absorbance spectra of the crystals via the synthesis of solid solutions with various contents of MII cations. The glass-ceramic synthetic approach is also proposed as a convenient method for the creation of new diphosphates, and the applicability of this method is verified for Cs3CaBi(P2O7)2. [ABSTRACT FROM AUTHOR]

The solid solution KNi0.93FeII0.07FeIII(PO4)2 {potassium [nickel(II)/iron(II)] iron(III) bis(orthophosphate)} has been prepared by the flux method. The compound shows a new type of structure for a phosphate with the general composition MI MII MIII(PO4)2. The framework is formed by [(Ni/Fe)O6] polyhedra [Fe site occupancy = 0.069 (14)] linked via shared oxygen vertices forming a cis-like parallel chain stretching along a and [FeO5] polyhedra (located on alternate sides of the chains) connected via two types of PO4 groups into a three-dimensional structure. The K atoms are disordered between two sites, denoted K1 A and K1 B, with occupancies of 0.930 (9) and 0.070 (9), respectively, and reside inside channels along the a axis. Calculations of the Voronoi-Dirichlet polyhedra of the K atoms give a coordination scheme for K1 A of [9 + 3] and for K1 B of [10 + 2]. The most remarkable feature of the structure is the splitting of the K-atom site and the population of the K1 A and K1 B positions due to substitution of Ni by Fe in the (Ni/Fe) position. [ABSTRACT FROM AUTHOR]

The solid solution KNi0.93FeII0.07FeIII(PO4)2 {potassium [nickel(II)/iron(II)] iron(III) bis(orthophosphate)} has been prepared by the flux method. The compound shows a new type of structure for a phosphate with the general composition MI MII MIII(PO4)2. The framework is formed by [(Ni/Fe)O6] polyhedra [Fe site occupancy = 0.069 (14)] linked via shared oxygen vertices forming a cis-like parallel chain stretching along a and [FeO5] polyhedra (located on alternate sides of the chains) connected via two types of PO4 groups into a three-dimensional structure. The K atoms are disordered between two sites, denoted K1 A and K1 B, with occupancies of 0.930 (9) and 0.070 (9), respectively, and reside inside channels along the a axis. Calculations of the Voronoi-Dirichlet polyhedra of the K atoms give a coordination scheme for K1 A of [9 + 3] and for K1 B of [10 + 2]. The most remarkable feature of the structure is the splitting of the K-atom site and the population of the K1 A and K1 B positions due to substitution of Ni by Fe in the (Ni/Fe) position. [ABSTRACT FROM AUTHOR]

Abstract: The crystallization of complex phosphates from the melts of Cs2O–P2O5–CaO–M III 2O3 (M III—Al, Fe, Cr) systems have been investigated at fixed value Cs/P molar ratios equal to 0.7, 1.0 and 1.3 and Са/Р=0.2 and Ca/М III=1. The fields of crystallization of CsCaP3O9, β-Ca2P2O7, Cs2CaP2O7, Cs3CaFe(P2O7)2, Ca9 M III(PO4)7 (M III—Fe, Cr), Cs0.63Ca9.63Fe0.37(PO4)7 and CsCa10(PO4)7 were determined. Obtained phosphates were investigated using powder X-ray diffraction and FTIR spectroscopy. Novel whitlockite-related phases CsCa10(PO4)7 and Cs0.63Ca9.63Fe0.37(PO4)7 have been characterized by single crystal X-ray diffraction: space group R3c, a=10.5536(5) and 10.5221(4)Å, с=37.2283(19) and 37.2405(17)Å, respectively. [Copyright &y& Elsevier]

Abstract: The single crystals of caesium magnesium titanium (IV) tri-oxo-tetrakis-diphosphate bis-monophosphate, Cs3.70Mg0.60Ti2.78(TiO)3(P2O7)4(PO4)2, crystallize in sp. gr. P-1 (No. 2) with cell parameters a=6.3245(4), b=9.5470(4), c=15.1892(9)Å, α=72.760(4), β=85.689(5), γ=73.717(4), z=1. The titled compound possesses a three-dimensional tunnel structure built by the corner-sharing of distorted [TiO6] octahedra, [Ti2O11] bioctahedra, [PO4] monophosphate and [P2O7] pyrophosphate groups. The Cs+ cations are located in the tunnels. The partial substitution of Ti positions with Mg atoms is observed. The negative charge of the framework is balanced by Cs cations and Mg atoms leading to pronounced concurrency and orientation disorder in the [P2O7] groups, which coordinate both. [Copyright &y& Elsevier]

Abstract: A new potassium bismuth phosphate-molybdate K2Bi(PO4)(MoO4) has been synthesized by the flux method and characterized by single-crystal and powder X-ray diffraction, IR spectroscopic studies. The compound crystallizes in the orthorhombic system with the space group Ibca and the cell parameters: a=19.7037(10), b=12.4752(10), c=7.0261(10). This phase exhibits an original layered structure, in which the [Bi(PO4)(MoO4)]∞ layers consist of [Bi2Mo2O18]∞ chains linked through single PO4 tetrahedra. The K+ cations interleaved between these layers exhibit a monocapped distorted cubic coordination. [Copyright &y& Elsevier]

Abstract: New complex phosphates of the general formula K2 M 0.5Ti1.5(PO4)3 (M=Mn, Co) have been obtained from the melting mixture of KPO3, K4P2O7, TiO2 and CoCO3·mCo(OH)2 or Mn(H2PO4)2 by means of a flux technique. The synthesized phosphates have been characterized by the single-crystal X-ray diffraction and the FTIR-spectroscopy. The compounds crystallize in the cubic system with the space group P213 and cell parameters a=9.9030(14)Å for K2Mn0.5Ti1.5(PO4)3 and a=9.8445(12)Å for K2Co0.5Ti1.5(PO4)3. Both phosphates are isostructural with the langbeinite mineral and contain four formula unit K2 M 0.5Ti1.5(PO4)3 per unit cell. The structure can be described using [M 2(PO4)3] framework composed of two [MO6] octahedra interlinked via three [PO4] tetrahedra. The Curie–Weiss-type behavior is observed in the magnetic susceptibility. [Copyright &y& Elsevier]

Polycrystalline potassium nickel(II) hafnium(IV) tris(orthophosphate), a langbeinite-type phosphate, was synthesized by a solid-state method and refers to langbeinite-type phosphates. The three-dimensional framework of the title compound is built up from two types of [MO6] octahedra [the M sites are occupied by Hf:Ni in ratios of 0.754 (8):0.246 (8) and 0.746 (8):0.254 (8), respectively] and [PO4] tetrahedra are connected via O vertices. The K+ cations are located in two positions within large cavities of the framework, having coordination numbers of 9 and 12. The Hf, Ni and K sites lie on threefold rotation axes, while the P and O atoms are situated in general positions. [ABSTRACT FROM AUTHOR]

The formation of complex phosphates is investigated in melts containing Rb2CO3, H3PO4, TiO2, and NiO at different molar ratios of Rb:P = 0.5-1.3, Ti:P = 0.15, Ti:Ni = 1.0 at 1073-953 K (Pt crucible, 1273 K, 3 h). [ABSTRACT FROM AUTHOR]