Abstract
An extensive study of the thermal properties of Lithium Sodium Sulphate Hexa hydrate (LSSW) single crystal, with Trigonal structure, has been carried out using ultrasonic Pulse Echo Overlap (PEO) technique, Differential Thermal Analysis (DTA) and Thermo Gravimetric Analysis (TGA). The temperature variation of elastic constants of LiNa3(SO4)2·6H2O single crystal have been reported for the first time. The second order elastic stiffness constants C11, C33, C44, along the various directions in the crystal have been determined in the temperature range 300 - 330 K. The change in velocity with temperature with respect to the room temperature value has been measured using PEO technique. Significant anomalies were observed in C11 and C33 at 316 K. The elastic constant C12 has shown no variation in the temperature range 300 - 319 K. A minor deviation for C44 at 305 K following a parabolic change has been observed. The minor anomalies observed in the elastic constants of LSSW may be due to its dehydration of water of crystallization in the range 304 - 319 K. DTA studies showed an appreciable endothermic change in the range 309 K-369.79 K. TGA curve exhibited a decrease in weight of 1.687 mg in the temperature range 304 K-360 K. The minor anomalies observed in the elastic constants of LSSW may be due to loosing of its water of crystallization in the range 309 - 319 K. On loosing water there will not be any change in chemical structure but there will be physical change associated with loosing of water molecule.
Highlights
Lithium Sodium Sulphate single crystal is an extensively studied super ionic crystal, which exhibits piezoelectric and pyro-electric properties
No investigation on phase transition has been conducted so far in the above room temperature range by any other method. Aim of this investigation is to investigate any anomalies in the elastic properties of the crystal by studying the variation of elastic properties of LSSW with temperature by ultrasonic Pulse Echo Overlap technique [4]
The diagonal elastic constants C11, C33, C44 have direct relationship with the suitable ultrasonic mode velocity given by Ci j = ρv2 where ρ is the density of the crystal and υ is the velocity of ultrasonic waves through the crystal
Summary
Lithium Sodium Sulphate single crystal is an extensively studied super ionic crystal, which exhibits piezoelectric and pyro-electric properties. In this family a new crystal LiNa3(SO4)2∙6H2O (LSSW) is synthesized This new sulphate salt characterized by the presence of water molecule in the unit cell, and it was reported [1]. No investigation on phase transition has been conducted so far in the above room temperature range by any other method Aim of this investigation is to investigate any anomalies in the elastic properties of the crystal by studying the variation of elastic properties of LSSW with temperature by ultrasonic Pulse Echo Overlap technique [4]
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