Congruent melting of tungsten phosphide at 5 GPa and 3200 °C for growing its large single crystals*

Abstract

As one of important members of refractory materials, tungsten phosphide (WP) holds great potential for fundamental study and industrial applications in many fields of science and technology, due to its excellent properties such as superconductivity and as-predicted topological band structure. However, synthesis of high-quality WP crystals is still a challenge by using tradition synthetic methods, because the synthesis temperature for growing its large crystals is very stringently required to be as high as 3000 °C, which is far beyond the temperature capability of most laboratory-based devices for crystal growth. In addition, high temperature often induces the decomposition of metal phosphides, leading to off-stoichiometric samples based on which the materials’ intrinsic properties cannot be explored. In this work, we report a high-pressure synthesis of single-crystal WP through a direct crystallization from cooling the congruent W–P melts at 5 GPa and ∼ 3200 °C. In combination of x-ray diffraction, electron microscope, and thermal analysis, the crystal structure, morphology, and stability of recovered sample are well investigated. The final product is phase-pure and nearly stoichiometric WP in a single-crystal form with a large grain size, in excess of one millimeter, thus making it feasible to implement most experimental measurements, especially, for the case where a large crystal is required. Success in synthesis of high-quality WP crystals at high pressure can offer great opportunities for determining their intrinsic properties and also making more efforts to study the family of transition-metal phosphides.