The heat capacity measurements of the crystalline trizirconium tetraphosphate were carried out in a low-temperature adiabatic vacuum calorimeter between T = (7 and 350) K and in dynamic calorimeter between T = (330 and 640) K. The experimental data were used to calculate the standard (p degrees = 0. 1 MPa) thermodynamic functions C degrees(pm)/R, Delta(0)(T)H degrees(m)/RT, Alpha(0)(T)S degrees(m)/R, and Phi degrees m = Delta(0)(T)S degrees(m) - Delta(0)(T)H degrees(m)/T (where R is the universal gas constant) in the range T -> (0 to 640) K. The fractal dimension D-fr for the crystalline phosphate Zr-3(PO4)(4) between T = (20 and 40) K was evaluated. From hydrofluoric acid solution microcalorimetry, the enthalpy of solution of Zr-3(PO4)(4) at T = 298.15 K was determined and the standard molar enthalpy of formation was derived. By combining the data obtained by the two techniques, the standard molar Gibbs function of formation of Zr-3(PO4)(4) at T = 298.15 K was calculated. (c) 2004 Elsevier Ltd. All rights reserved.