Measurement of Anisotropic Compressibilities by a Single Crystal Diffractometer Method*

Abstract

AbstractThe beryllium diamond-anvil pressure cell described by Weir, Piermarini and Block has been mounted on a Bond diffractometer equipped with an orienter of the fixed-x type. Molybdenum radiation is used to penetrate the diamonds and beryllium of which the cell is constructed, and special techniques are required to retain adequate precision in measuring cell parameters using diffraction angles in the low 2θ range. The method described provides high sensitivity in determining peak positions and eliminates the effect of centering errors on measured values of 2θ. Under favorable conditions, diffraction angles are measured with an accuracy of ±0.001° in 2θ. The method has been tested by measuring the lattice parameter of vacuum float zone refined silicon. Measurements of the compressibilities of silicon and of α-Pb(N3)2 (orthorhombic) have been carried out using the method of Barnett, Block, and Piermarini to determine pressure by measuring the shift in the R-line fluorescence spectrum of ruby.