Physical properties of YB66 and consideration of possible use for high-resolution X-ray optics

Abstract

A combined microscopic, i.e., powder and single crystal x-ray diffraction and inelastic x-ray scattering, and macroscopic, i.e., heat capacity, characterization was carried out on YB66 between 10 and 400K. The system crystallizes in a rather large unit cell with a lattice parameter of about 23.4Å at room temperature. The volume thermal expansion coefficient is found to be 3.9×10−5K−1 at 295K. A high Debye temperature above 1000K was determined using several methods, 1043(25)K, from heat capacity measurements, 1430(59)K, from elastic constants measurements, and 1690(198)K, from thermal expansion measurements. The thermal transport is modeled as a collection of Einstein oscillators with an Einstein temperature of 194(2)K. The C11 and C44 elastic constants are above 400 and 150GPa, respectively. The average speed of sound in YB66 is estimated to be 9631(380)m/s, similar to the average speed of sound in corundum, 10000m/s. The large volume of the unit cell and the stiffness of the crystal structure make YB66 a promising candidate for high-resolution x-ray monochromatization applications. Candidate reflections for high-resolution resonant inelastic x-ray scattering are indicated and potential pitfalls relevant to the quality of crystals and multi-beam cases are mentioned.