Icosahedral hydrides of the Ti45Zr38Ni17−xCox nano-powders

• The synthesized Ti45Zr38Ni(13,9)Co(4,8) samples behave similarly to Ti45Zr38Ni17.
• The phase transformation into the i-phases at the similar temperatures.
• The hydrogen concentration in the i-phases is higher than in the amorphous powder.
• The hydrogen capacity in the i-phase with Co8 is higher than in the basic structure.
• The icosahedral nano-powders were reversibly hydrogenated and dehydrogenated.

In this communication we report the phase transitions associated with a hydrogen uptake in the quasicrystalline Ti45Zr38Ni17−xCox alloys that were prepared by mechanical alloying. The crystal structure evolution of the alloys was characterized by means of the variety of diffraction techniques (X-ray, neutron, and electron) as well as extended X-ray absorption fine structure spectroscopy (EXAFS). That analysis was supported by the results of the thermodynamic measurements, namely differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS).According to the neutron diffraction results, the transformation of the amorphous Ti45Zr38Ni17−xCox phases into the quasicrystalline state starts at the temperature of 475 °C. At 525 °C the icosahedral phase (the i-phase) is well-developed. At higher temperatures the i-phase transforms into the approximant w-phase and eventually into the cubic phase (the c-phase).The investigated icosahedral nano-powders exhibit a high capacity for gaseous H2 reaching 2.2 wt.% at elevated temperatures. After a hydrogen uptake, a complex phase constitution including the simple hydrides is evidenced. Although the i-phases form again after hydrogen desorption, they are accompanied by the additional Zr3Co phase.

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