The positive muon in the intermetallic hydride ZrV2Hx: A muon tracer study supplemented by differential thermoanalysis, neutron vibrational spectroscopy, and quasielastic neutron scattering

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Abstract
ZrV2 is an intermetallic compound with energetically different interstitial sites, which upon hydrogenation are successively filled with hydrogen (thermodynamic distribution). When a positive muon is added as a microscopic probe, it is thermalized at random and thus at low temperatures statistically distributed over the available (unblocked) interstices. By varying the preloading we scan the accessible hydrogen sites and find that at high hydrogen content three kinds of interstices are occupied, in contradiction to literature diffraction data. This surprising result is confirmed by a detailed neutron vibrational spectroscopy study on ZrV2Hx which is presented as well. The temperature dependence of the μ+ relaxation rate is textbook‐like in empty ZrV2: static muon at T200 K. In ZrV2Hx, however, the relaxation rate exhibits an intermediate plateau which we attribute to a relocation of the muon. The motion of the muon above 150 K is interpreted as being directly related to the hydrogen diffusion which we have separately measured by means of quasielastic neutron scattering. In addition, we investigated the ZrV2/H phase diagram by differential thermoanalysis.