High Pressure Polymorphism in Cesium.

A new polymorph of cesium, existing over the narrow pressure range from about 42.2 to 42.7 kilobars at room temperature, has been discovered. Its crystal structure is face-centered-cubic with a = 5.800 +/- 0.007 A at 42.5 kb and 27 degrees C. Cesium-II, which exists over the pressure range 23.7 to 42.2 kb, is also face-centered-cubic with a = 5.984 +/- 0.011 A at 41 kb and 27 degrees C. An improved resistance-pressure curve and x-ray compressibility measurements for Cs are also given.