Louis, Godfrey; Philip, J(The American Physical Society, 1996)
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Abstract:
A detailed ultrasonic study of the elastic properties of lithium ammonium sulfate ~LiNH4SO4! or LAS has
been carried out below room temperature. The elastic constants of LAS at room temperature are reported. The
discrepancy present in earlier elastic constant data associated with the different choice of axes for this orthorhombic
system are clarified. The results of the temperature variation study down to 220 K confirm the
ferroelastic phase transition at 285 K and establish a thermal hysteresis of about 2.5 K between the cooling and
heating cycles. Results of the investigation on the suspected weak phase transition at 256 K suggest that this
transition occurs at 242 K on cooling and at 256 K on heating, thus having a thermal hysteresis of about 14 K.
However, since the observed elastic anomaly for this transition is very small, the nature of this transition still
remains unclear