Detection of anomalies in NLO sulphamic acid single crystals by ultrasonic and thermal studies

摘要

The ultrasonic pulse echo overlap technique (PEO) has been used to measure the velocities of 10 MHz acoustic waves in sulphamic acid single crystals in the range of 300-400 K. This study evaluated all the elastic stiffness constants, compliance constants and Poisson's ratios of the crystal. The temperature variations of the elastic constants have been determined. The phase transition studies above room temperature were investigated using ultrasonic PEO technique. This study has suggested new weak elastic anomalies for the crystal around 330 K. The transverse elastic constants C (44) and C (66) have shown clear thermal hysteresis of 2 K. The present differential scanning calorimetric (DSC) studies carried out at a slow heating rate have also suggested weak phase transition around 331 K. The present elastic and thermal studies have been substantiated by already reported DC electrical conductivity studies around 330 K.