Nonvariant polymorphic transition from hexagonal to monoclinic lattice in GaTe single crystal

Abstract The polymorphic transition from hexagonal to monoclinic phase was studied for the first time in melt grown GaTe crystals. The polymorphic transition goes as a non-variant process at a constant temperature and pressure without any changes in composition. Though the character of the phase transition is apparently diffusive, no interface or grain boundaries are detected. After completion of the phase transition the whole volume of the crystal remains a single crystal. The cleavage plane is preserved and proves to be a habit plane between the hexagonal and monoclinic phase. Reflections in Laue patterns are sharpened and peaks in X-ray diffraction patterns are narrowed upon the transition, which is attributed to relaxation of internal stresses. Annealing of the transformed monoclinic GaTe at 1023K followed by quenching does not incite decomposition of the compound, which is explained by high stoichiometry of the grown crystal. Energy gap value after storage at room temperature and after the annealing is 1.65 eV, which corresponds with the data for monoclinic GaTe. The Vickers microhardness is 360 MPa.