Ultrasonic measurement of the elastic constants of sodium p-nitrophenolatedihydrate single crystals

Sodium p-nitrophenolate dihydrate single crystals possess excellent nonline ar optical properties such that they can be used for optical second-harmoni c generation. It belongs to the orthorhombic system with the space group Im a2. Slow evaporation or slow cooling techniques can be used to grow good op tical quality single crystals from supersaturated solution. All the nine el astic constants of this crystal have been measured using an ultrasonic tech nique. Samples for measurements have been cut along desired crystallographi c axes and the pulse echo overlap technique has been used to measure longit udinal and shear ultrasonic wave velocities along appropriate symmetry dire ctions in the crystal. The McSkimin Delta t criterion has been applied to d etermine the round trip travel time accurately, from which the nine elastic constants have been evaluated. Temperature variation of selected elastic c onstants in a limited range have also been measured and reported.