Dilatometric investigations of phase transitions in TEA2MnCl4 crystals

Results of dilatometric measurements of [N(C2H5)(4)](2)MnCl4 single crystal along the main crystallographic axes in the temperature range of 170 divided by 240 K are presented. The positive thermal deformation in b direction and the negative one in c direction were found. Anomalies in the thermal expansion and the thermal hysteresis confirm the first-order character of both phase transitions. The changes in the relative crystal volume at the phase transition temperatures (Delta V/V-228 (K)= 0.032 and Delta V/V-224 (K)= 0.022) were determined on heating. Based on the dilatometric and specific heat data the coefficients of the pressure dependent shift of the transition temperature were estimated for both phase transition temperatures. These are Delta T-1/Delta p congruent to 0.9 K/MPa and Delta T-2/Delta p congruent to 0.3K/MPa. The roentgenographic data collected for the high-temperature phase as well as low-temperature phases could not be interpreted unambiguously.