A COMPARATIVE-STUDY OF THE 2ND-ORDER BIRCH AND MURNAGHAN EQUATIONS OFSTATE FOR IONIC SOLIDS

A comparative study of the Birch equation of state (BES) and the Murna ghan equation of state (MES) is presented for ionic solids including a lkali halides, silver halides, thallous halides, cuprous halides, alka line earth fluorides and oxides. The higher order terms containing the second order pressure derivative of bulk modulus are also included an d evaluated from the interionic potentials. Both the equations of stat e are used to predict the pressure and volume relationship for twenty- six ionic crystals. The results are found to compare well with the ava ilable experimental data in the low pressure region for LiF, NaF, CsCl , and AgBr crystals. A critical comparison of the compression (P-V) va lues estimated from various equations of state is presented for Csl fo r which the experimental static compression data are available for hig h pressure range. The second order Birch equation of state presents th e best agreement with the experimental data.