Elastic properties of sodium doped Lithium potassium sulphate, LiK0.9Na0.1SO4, crystal has been studied by
ultrasonic Pulse Echo Overlap [PEO] technique and are reported for the first time. The controversy regarding
the type of crystal found while growth is performed at 35 °C with equimolar fraction of Li2SO4H2O, K2SO4
and Na2SO4 has been resolved by studying the elastic properties. The importance of this crystal is that it
exhibits pyroelectric, ferroelectric and electro optic properties. It is simultaneously ferroelastic and
superionic. The elastic properties of LiK0.9Na0.1SO4 crystal are well studied by measuring ultrasonic velocity
in the crystal in certain specified crystallographic directions and evaluating the elastic stiffness constants,
compliance constants and Poisson’s ratios. The anisotropy in the elastic properties of the crystal are well
explained by the pictorial representation of the surface plots of phase velocity, slowness and linear
compressibility in a-b and a-c planes.