ZrNi–H 2: microstructural analysis of the thermodynamically controlled hydride phase growth, and electronic properties

Abstract

The ZrNi–H 2 phase diagram indicates the presence of two stable hydrides: a triclinic monohydride ZrNiH and an orthorhombic trihydride ZrNiH 3 [1]. In this paper, we present the results of some thermodynamic, microstructural and electronic properties of the ZrNi–H 2 system. A strict control of the thermodynamic variables ( P, T) during the hydride phase growth allowed us to prepare two samples of overall composition ZrNiH 0.70 and ZrNiH 2.5. In a first step, the microstructure evolutions induced by hydrogen absorption are investigated during the activation process. The intermetallic and hydrided compounds are studied by energy dispersive X-ray spectroscopy (EDXS) and X-ray diffraction (XRD) methods. The nature of defects generated in ZrNi and its hydrides compounds are observed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Ab-initio electronic structure calculations have been performed. They clearly show the importance of chemical effects besides geometrical factors in explaining the preferential site occupancy of hydrogen atoms in the ZrNiH phase.