Synthesis, structure, and superconductivity of new high pressure phases in the systems GeP and GeAs

Abstract

Reactions of Ge with P and As were run in a tetrahedral anvil press at conditions ranging from 600–1300C and 15–65 kbars. Three new phases were found in the GeP system. Two phases of approximate formulas GeP 5 and GeP 3 have rhombohedral crystal structures related to the A7 arsenic type. The cell dimensions of GeP 5 are a = 3.467 (3)Å, c = 10.04 (1)Å and of GeP 3 a = 7.050 (1)Å, c = 9.932 (3)Å. The cell dimensions vary for different preparations indicating ranges of stoichiometry. A new tetragonal form of GeP was prepared by the reaction of Ge + 1.0–1.7 P at 600–800C, 45–65 kbars. The cell dimensions are a = 3.544 (2)Å, c = 5.581 (1)Å and space group is 14 mm. A similar tetragonal phase was formed in the GeAs system. The cell dimensions are: a = 3.715 (1)Å, c = 5.832 (1)Å. The tetragonal crystal structures were solved by least-squares refinement of the powder-diffraction intensity data. Bond distances and angles were calculated. Electrical measurements on single crystals show metallic behavior. Meissner effect measurements show that GeP is superconducting below 1.8–4.2K and GeAs below 3–3.5K.