Thermal Expansion in the Zr and 1-, 2-valent Complex Phosphates of NaZr2(PO4)3 (NZP) Structure

A_5–4xZr_xZr(PO₄)₃ (A=Na, K;0≤x≤1.25), Na_1-xCd_0.5xZr₂(PO₄)₃ (0≤x≤1), Na_5–xCd_0.5xZr(PO₄)₃ (0≤x≤4) compositions which belong to the NZP structural family were synthesized using the sol-gel method. The lattice thermal expansion of members of these rows were determined up to 600°C by high-temperature X-ray diffractometry. The axial thermal expansion coefficients change from -5.8·10^-6to 7.5·10^-6 °C^-1 (α_a) and from 2.6·10^–6 to 22·10^–6 °C^-1 (α_c). These results, in addition to those for other NZP compounds allow us to explain their low thermal expansion. The mechanism can be attributed to strongly bonded three-dimensional network structure, the existence of structural holes capable to damp some of the thermal vibrations and anisotropyin the thermal expansion of the lattice. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermal Expansion of Mixed Zirconium Phosphates

A series of framework phosphates with varied ratio of cations Na_5-2x B _x ^IIZr(PO₄)₃, B^II = Mg, Ca, Sr, Ba (0 x 2) and Na_5-3x Fe _x Zr(PO₄)₃ (0 x 1.33) were synthesized and studied under heating. The coefficients of thermal expansion along crystal axes _a and _c were calculated, and their dependences on the cationic composition (nature and concentration) and on the occupancy of out-of-framework structural positions were established.     

Synthesis and Thermal Expansion of Complex Niobium(V) Phosphates with Bivalent Elements

Thermal expansion of niobium phosphates, new representatives of the family of structural analogs of [NaZr₂(PO₄)₃], was studied. These compounds possess high thermomechanical stability because of the unique ability of their structure to expand-contract along different crystallographic directions under thermal treatment.     

Synthesis and Characterization of Niobium-Bearing Members of the NZP and NbOPO 4 Structural Families

Theoretically predicted by us, M 1/3 Nb 5/3 (PO 4 ) 3 (M = Mg, Mn, Co, Ni, Cu or Zn) compounds with the sodium zirconium phosphate (NZP) framework structure having no interstitial ions were synthesized. The rising of temperature above 900;C causes the change of chemical composition of NZP compounds and formation NbOPO 4 -like products. The phase formation regularities stated gave a possibility to choose optimal conditions for preparation of these phosphates.     

Thermodynamic Properties of the MZr2(PO4)3 (M=Na,K, Rb or Cs) Compounds

The enthalpies of the solution of MZr₂(PO₄)₃(M=Na, K, Rb or Cs) compounds have been measured by the help of a differential automatic isothermal Calvet calorimeter and the standard enthalpies of formation have been derived. The temperature dependencies of the standard heat capacity of the samples of crystalline NaZr₂(PO₄)₃ and CsZr₂(PO₄)₃ were studied between 7 and 340 K in an automatic adiabatic vacuum calorimeter. The main thermodynamic functions H ⁰(T)–H ⁰(0), S ⁰(T) andG ⁰(T)–H ⁰(0) have been determined. The Gibbs energies of formation of the NaZr₂(PO₄)₃and CsZr₂(PO₄)₃ at 298.15 K were calculated on the basis of these experimental data and the enthalpy of formation data. Qualitative explanations for the results observed were presented. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat Conductivity of Zirconium and Alkali Metal (Na,Cs) Phosphates of the NaZr2(PO4)3 Family

The heat conductivity of porous Zr₃(PO₄)₄, NaZr₂(PO₄)₃, CsZr₂(PO₄)₃, and Na₅Zr(PO₄)₃ samples was studied in the range 298-673 K. The heat conductivity coefficients of the zero-porosity phosphates under study were calculated and prospects for their application were considered.