The temperature dependence of the specific heat Cp and the electrical resistivity ρ of pure lithium-ammonium sulphate (LAS) single crystals along the three principal crystallographic directions is investigated in the 300-500 K temperature range. The transition energy ΔQ and the number of both elementary (No) and thermally excited (Ne) dipoles are calculated. It appears that only a small fraction of the total number of dipoles is capable of being thermally excited in the ferroelectric phase. The correlation between the Cp data and the spontaneous polarization Ps is verified. The J-E characteristics indicate the possibility of space charge effects at low measuring fields. Anomalous behaviours before and at the transition point is observed. Thermal annealing is found to be necessary for reproducible results. The temperature dependence of ρ long the polar axis yields the values ΔE = 0.54 and 1.48 eV and ΔE = 1.95 eV for the energy activating the charge transport mechanisms in the ferro- and the paraelectric phases, respectively. A pre-transition phenomenon is observed while measuring both Cp and ρ along the a- and the b-axes. The mechanism of electrical conduction in the measuring range is discussed. Along the polar axis Cp of LAS crystals doped with either Cu2+, Co2+, Ni2+ or Mn2+ is measured in the same temperature range. Above Tc, the temperature range through which log Cp is linearly proportional to (T - Tc) is wider than that predicted theoretically. The transition energy, the fraction Ne/No and Ps are also calculated for doped crystals

The d.c.,electrical resistivity, , of pure LiNH4SO4 single crystals has been measured between 300 and 500 K in three successive runs. Anomalous behaviour before and at the transition point was observed and thermal annealing was necessary for reproducible results. The temperature dependence of along the polar axis yielded the values E=0.54 and 1.48 eV and E=1.95 eV for the energy activating the charge transport mechanisms in the ferroelectric and the paraelectric phases, respectively. A pre-transition phenomenon was observed while measuring along the a- and b-axes. The J-E characteristics indicated possible space-charge effects at low measuring fields. The mechanism of electrical conduction in the measuring range has been discussed

The d.c.,electrical resistivity, , of pure LiNH4SO4 single crystals has been measured between 300 and 500 K in three successive runs. Anomalous behaviour before and at the transition point was observed and thermal annealing was necessary for reproducible results. The temperature dependence of along the polar axis yielded the values E=0.54 and 1.48 eV and E=1.95 eV for the energy activating the charge transport mechanisms in the ferroelectric and the paraelectric phases, respectively. A pre-transition phenomenon was observed while measuring along the a- and b-axes. The J-E characteristics indicated possible space-charge effects at low measuring fields. The mechanism of electrical conduction in the measuring range has been discussed