The heat capacity function C-p,m(o)=f(T) of crystalline CsNiPO(4 )was measured between 6 K and 650 K. A heat capacity anomaly was found around 382.8 K due to a phase transition. The experimental data obtained were used to calculate the standard thermodynamic functions C-p,m(o)/R, Delta H-T(0)m(o)/RT, Delta S-T(0)m(o)/R and Phi(o)(m)/R in the range from T=(5 to 650) K, and the standard entropy of formation at 298.15 K. The fractal dimension of CsNiPO4 was calculated from experimental data on the low-temperature (6 <= T <= 50) K heat capacity and the topology of the phosphate structure was estimated. The crystal structure of caesium-nickel monophosphate was investigated. Thermal expansion parameters were determined with high-temperature X-ray diffraction measurements in the temperature range from T = (473 to 1073) K. (C) 2018 Elsevier Ltd.