High-Pressure Forms of CsNiF3

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Abstract
The atmospheric pressure form of CsNiF3 consists of hcp layers of CsF3 with F6 octahedra face‐shared to form infinite chains along the c axis. CsNiF3 transforms at ∼5 kbars to a 9‐layer stacking sequence with ⅔ of the layers hcp and ⅓ of the layers ccp while at ∼50 kbars it transforms to a 6‐layer stacking sequence with ⅓ of the layers hcp and ⅔ of the layers ccp. Once formed, these phases are stable at atmospheric pressure to several hundred degrees C. The 9‐layer phase is paramagnetic above 80°K with μeff=3.2 μB and Θp=−75°K. Trace amounts of a ferromagnetic material prevented further analysis below 80°K. The light‐yellow 6‐layer phase shows a ferrimagnetic Tc=111°K and a dTc/dp=0.53°K/kbar. The magnetic and optical properties are very similar to the isostructural RbNiF3.