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The heat capacity (C), magnetic susceptibility (χ), and magnetization (M) of Eu5Sn3S12 are investigated. C is measured by a vacuum adiabatic calorimeter (T = 2 to 300 K). Three anomalies are found in the C(T) dependence: two maxima at 4 and 7K and a bend at 3K. The thermodynamic functions S2 to 298.15 K = 724 J/mol K and H2 to 298.15 K = 97.70 kJ/mol are calculated. Magnetic properties are investigated by a vibrating sample magnetometer in fields up to 30 kOe in the temperature range 1.7 to 200 K. The existence of two field‐dependent antiferromagnetic phases in Eu5Sn3S12 are found at low temperatures (< 7 K). 1/χ(T) is linear above 35 K (CM = 27, θp = −2.5 K). The M(H) behaviour is of step character inherent to metamagnetism.

It is shown that crystals with the symmetry m 3 and m 3m are suitable materials to study if one is seeking to detect the dependence of electrogyration on stress which is described by an axial tensor of rank five. Experiments are performed on methylammonium alums doped with chromium. Several properties of the material enable critical checks of experimental results to be made. The checks are needed because the intrinsic effect is usually smaller than effects which are caused by the interaction of linear and circular optical properties but which are no signature of intrinsic piezo-electrogyration. At room temperature a stress-induced electrogyration of 6 × 10-17 V-1 Pa-1 has been observed. At a temperature of 200 K which is 25 K above the transition into the ferroelectric phase the magnitude of the stress-induced circular electrodichroism is 10-15 V-1 Pa-1 in a sample with 10% chromium. These magnitudes are considered to represent upper limits of piezo-electrogyration in crystals because they result from special properties of the doped alum.

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Measurements of the dielectric constants E,, E,, and E, as a function of temperature showed dielectric anomalies at T,. = 269.6 K in orthorhombic crystals KZGe80,, (KGO). Soft modes and Fano-type effects were observed in polarized Raman spectra above T,. We assume that below T, the crystal structure of KGO may be described by the polar point group CJm) with spontaneous polarization lying in the mirror plane. The phase transition may be qualitatively described by the order parameter q(Bzs) which interacts with polarization components Pa(B3J and PJB,").