EQUATION OF STATE FOR CESIUM METAL TO 23-KBAR

An experimental equation of state has been determined for cesium metal at temperatures from 20° to 280°K and at pressures up to 23 kbar. The results can be expressed analytically over the range 41-67 cm3/mole to an accuracy of 0.2 cm3 by the relationship P(V, T) = ( 21.5 2.84) [( 66.5 V)2.84-1] + 3.65 × 10-3(T- 10°K) kbar, where V is measured in cm3 mole. This relationship assumes that the isothermal bulk modulus is a function of volume only, that (∂BT/∂P)T = 2.84, independent of temperature and volume, and that the molar volume and bulk modulus at T = 0 and P = 0 are respectively V0 = 66.5 cm3 and B0 = 21.5 kbar. A summary is given of similar parameters for the other alkali metals. This summary emphasizes the differences (on a reduced scale) between the equations of state for Li, Na, K and Rb (for which (∂BT/∂P)T ∼ 3.8), and for cesium. The relatively greater softness of the P-V relation for cesium possibly is due to the extreme sensitivity to compression of the electronic band structure of this metal. Transition parameters are given also (from 77° to 300°K) for the CsI-II transition which occurs at approximately 22.4 kbars at room temperature. © 1969.