Tatyana Victorovna Filippova

CeNi3-based Intermetallic hydrides

A hydride phase containing 5.0 H atoms per formula unit has been synthesized in the CeNi3-H2 system at a hydrogen pressure of 5 MPa and a temperature of 273 K. The hydride is very stable during storage in air, with no hydrogen release. Its lattice parameters have been determined by X-ray diffraction for different synthesis conditions.

LaNi5- and RT3-based (R = Ce, Nd, Gd, Er; T = Co, Ni, Fe) hydrides prepared at low temperatures and H2 pressures

Hydride phases based on the intermetallic compounds LaNi5, CeCo3, NdNi3, GdFe3, DyCo3, and ErNi3 have been synthesized at a hydrogen pressure of 10 MPa and a temperature of 273 K. The phase composition of the synthesized materials and the lattice parameters of the hydride phases have been determined by X-ray diffraction. During storage in air at room temperature, the hydrides decompose more slowly than do their analogs synthesized at low pressure. The hydrogen content of the hydrides is higher than or similar to that of hydride phases synthesized at high pressure. X-ray diffraction results for the low-temperature RT3-based intermetallic hydrides demonstrate that their lattice is expanded to a lesser extent than that of their high-pressure analogs.

Interaction between Intermetallic Compounds RNi3 (R = Gd, Dy) and Hydrogen at Low Temperatures

The hydride phases of the intermetallic compounds GdNi3 and DyNi3 are synthesized at room temperature and at 273 K under a hydrogen pressure of 1–30 bar. The phase composition of the obtained samples is established using the X-ray diffraction method and the crystal-lattice parameters of the hydride phase are determined. The crystal phases are synthesized at room temperature under a hydrogen pressure of about 1 bar. At 273 K and under a pressure of 30 bar, amorphous samples are formed. The desorption of hydrogen from amorphous hydrides at 573 K leads to the formation of well-crystallized samples of the initial intermetallides. The amorphous samples are formed due to the ordering of hydrogen atoms in the metallic matrix of the hydride at low temperatures.

On the structure of stable CeNi3 based hydrides

The structure of stable hydrides of CeNi3 intermetallic compounds synthesized at low temperatures is studied by the neutron diffraction method. The phase composition of the hydride samples and the hydrogen site distribution in each phase are determined. It is established that hydrogen mainly occupies vacancies in the lattice of the hydride phase, while the lattice of the intermetallic phase contains a small amount of hydrogen.

Structure of Partly Vacuum Extracted MgH2 Samples

The structure of partly desorbed and quenched samples of MgH2 has been investigated by the neutron diffraction method. In ambient conditions a partly desorbed sample demonstrates high stability, while the same sample quenched at low temperature decomposed into Mg after several days. Obtained neutron data showed that all studied samples contain coexisting Mg and MgH2 phases. Hydrogen distribution for both quenched and non-quenched samples is similar. Hydrogen atoms occupied sites predominantly in the MgH2 lattice, whereas Mg lattice is free of the hydrogen.

Stability of MgH2 Samples after Thermodesorption

Samples of partly desorbed MgH2 have been studied by the X-ray diffraction method. All samples contained two phases (Mg and MgH2) and were stable at ambient condition for several months. After fast quenching in liquid nitrogen the samples became unstable and transformed after several days into Mg. The rate of decomposition depends on the amount ratio of Mg and MgH2 phases in the sample. Destabilization of the hydride phase observed in quenched samples can be explained on the basis of different diffusion of disordered and ordered hydrogen atoms.

Hydrogen Behavior in NdRh3-based Hydrides

Samples of desorbed NdRh3-based hydrides have been investigated by the X-ray diffraction method. X-ray data analysis showed that the samples contain two phases with hexagonal and cubic lattices. It was revealed that proportion of these phases in the samples depends on the rate of heating before the hydrogen desorption. At high rates of the heating in the desorbed samples amount of the phase with cubic lattice increased. This behaviour of the hydrogen in hydrides can be explained by the difference in the diffusion of disordered and ordered hydrogen atoms.

Stability of CeCo3-based intermetallic hydrides

CeCo3-based intermetallic hydride samples have been synthesized at hydrogen pressures in the range from 0.1 to 10 MPa at room and low temperatures. The phase composition and lattice parameters of the synthesized hydride phases have been determined by X-ray diffraction. The hydrides have been shown to differ in stability. Some of the samples were stable and did not lose hydrogen during storage in air at room temperature for several months, and some decomposed under the same conditions and lost hydrogen in several minutes. This behavior of the hydride phases depends on synthesis conditions (pressure and temperature) and the quantitative relationship between the α-solid solution and the β-hydride phase in the samples.

The Stability of CeNi3-Based Intermetallic Hydrides

Hydrides of CeNi3 intermetallic compounds were synthesized with hydrogen at a pressure of up to 50 bars at room and low temperatures. Using the X-ray diffraction method gives phase composition and lattice parameters of the hydride samples. It was revealed that one set of the hydride samples was stable in air and at room temperature, while another set was very unstable at the same conditions and rapidly desorbed hydrogen. This diverse behaviour depends on the proportion of obtained hydride phases at low and room temperatures, coexisting in the samples. A possible explanation has been proposed based on the different diffusion of hydrogen atoms in ordered and disordered hydride phases, incorporated in the samples.

NdRh3-based intermetallic hydrides

We have studied chemical interaction of the intermetallic compound NdRh3 with hydrogen at pressures of up to 0.2 GPa. The structural changes in the intermetallic matrix in different stages of the hydrogenation process have been followed using synchrotron X-ray diffraction. The results demonstrate that hydrogen absorption leads to an irreversible change in lattice symmetry from hexagonal to cubic.