Data on synthesis, thermal behavior and thermodynamic properties for the NZP phosphates NaMe2(PO4)3 and Na5Me(PO4)3 (Me=Ti, Zr, Hf) are reported. The compounds were synthesized by sol-gel method and solid-state reactions and characterized by
X-ray powder diffraction, IR spectroscopy, electron microprobe and chemical analysis. Their thermal behavior was studied by
the DTA measurements. The heat capacities of the phosphates were measured between temperatures 7 and 650 K. The fractal dimensions
for the phosphates were calculated. The obtained thermodynamic characteristics of these phosphates and also literature data
for the compounds of NZP type structure are summarized.
A5–4xZrxZr(PO4)3 (A=Na, K;0≤x≤1.25), Na1-xCd0.5xZr2(PO4)3 (0≤x≤1), Na5–xCd0.5xZr(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 600C by high-temperature X-ray diffractometry. The axial thermal
expansion coefficients change from -5.810-6to 7.510-6 C-1 (αa) and from 2.610–6 to 2210–6 C-1 (αc). 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.
The temperature dependence of the heat capacity of crystalline barium zirconium phosphate Cpo = f(T) was measured over the temperature range 6–612 K. The experimental data obtained were used to calculate the standard thermodynamic functions Cpo(T), H°(T) − H°(0), S°(T), G°(T) − H°(0) over the temperature range from T → 0 to 610 K and standard entropy of formation at 298.15 K. The data on the low-temperature (6 ≤ T/K ≤ 50) heat capacity were used to determine the fractal dimension of Ba0.5Zr2(PO4)3. Conclusions concerning the topology of the structure of phosphate were drawn. Thermodynamic properties of M0.5Zr2(PO4)3 (M = Ca, Sr, Ba) were compared.
Summary The thermodynamic data for NZP compounds MZr2(PO4)3 (M=Na, K, Rb, Cs, Zr0.25) and Na5D(PO4)3 (D=Ti, Zr) are reported. The heat capacities of the phosphates were measured between T=7 and T=640 K. The standard enthalpies entropies, and Gibbs functions of formation at T=298.15 K were derived. The obtained thermodynamic characteristics of phosphates of the NZP type structure and literature data are summarized. Thermodynamic functions of reactions of solid-state synthesis were calculated and the usability of ceramic technology for obtaining NZP compounds was proved.