Electronic Properties of MoSi2-Type Hf2X Intermetallic Compounds (X=Pd,Ag, Cd)

The Hf z coordinate and the value of the electric field gradient (efg) main component (V _zz ), were calculated for three Hf₂X compounds (X = Pd, Ag, Cd) on a first-principle basis, using the full potential linear augmented plane wave (LAPW) method. Exchange and correlation effects were treated either by the local spine density approximation (LSDA) or by the more advanced generalized gradient approximation (GGA). The calculated V _zz values, in the Hf site, were in very good agreement with available ¹⁸¹Hf TDPAC experimental results. This revised version was published online in September 2006 with corrections to the Cover Date.     

High Pressure Study of HfNi Crystallographic and Electronic Structure

The crystallographic structure and electronic properties of HfNi were studied as a function of pressure by combining X-ray diffraction results with the full potential linearized augmented plane wave (LAPW) calculations. No phase transition was observed up to a pressure of 35.3 GPa, with a total volume contraction of V/V ₀ = 0.85, a bulk modulus value of B ₀ = 52 ± 3 GPa and B ₀ ^′ = 1.29 ± 0.26. The calculated linear increase in the V _zz value as a function of the pressure induced volume reduction at the hafnium site was attributed mainly to the p–p contribution, while in the nickel site, a non negligible d–d contribution to V _zz is also observed, and attributed to the high 3d-partial DOS near the nickel nucleus. Based on the total electronic DOS at E _Fermi calculated for 0 K (N(E ⁰ _Fermi)), a value of 6.85 and 5.03 (mJ/mol/k²) was calculated for the band contribution (γ _band) to the electronic specific heat coefficient (γ) at a pressure of 0 and 35.3 GPa, respectively.     

XRD, TDPAC and LAPW study of Hf10B2 under high pressure

The crystallographic structure and electronic properties of Hf¹⁰B₂ were studied as a function of pressure by combining X-ray diffraction measurements with full potential linearized augmented plane wave (LAPW) calculations. No phase transition was observed up to a pressure of 30.8 GPa, with a total volume contraction of V/V ₀?=?0.85 and a bulk modulus value of B ₀?=?232 ±13 GPa. The calculated V _zz value at the hafnium site is linearly increasing as a function of the pressure induced volume reduction, while the V _zz value at the boron site stays almost zero. The major contribution to the V _zz value at the hafnium site comes from a p–p contribution next to the probe nucleus, with a relatively large d–d contribution of about 25%. This unusual large d–d contribution arises from the hafnium p–d electrons coupling.     

TDPAC study of the ZrCo-hydrogen system

The properties of the ZrCo-hydrogen system as a function of composition ratio H/ZrCo were investigated by combining TDPAC and X-ray diffraction techniques with the full potential linearized augmented plane wave (LAPW) band structure calculations. It was found that during hydrogenation ZrCo transferred directly into ZrCoH₃ and no transition phase existed. The z component V_zz of the efg and the asymmetry parameter η at the Zr and Co sites were calculated for ZrCoH₃ by using the structure parameters of Zr and Co, obtained in the present work, combined with the hydrogen structure parameters obtained from neutron diffraction on ZrNiH₃. The calculations are in good agreement with the measured values for V_zz and η. This agreement is consistent with the proposed 4c and 8f interstitial sites occupancy of the hydrogen atoms in ZrCoH₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

Substitution tilings and separated nets with similarities to the integer lattice

We show that any primitive substitution tiling of ℝ² creates a separated net which is biLipschitz to ℤ². Then we show that if H is a primitive Pisot substitution in ℝ ^d , for every separated net Y, that corresponds to some tiling τ ∈ X _H , there exists a bijection Φ between Y and the integer lattice such that sup _y∈Y ∥Φ(y) − y∥ < ∞. As a corollary, we get that we have such a Φ for any separated net that corresponds to a Penrose Tiling. The proofs rely on results of Laczkovich, and Burago and Kleiner.     

Electronic properties of Hf2X intermetallic compounds (X = Al, Si, Ni, Ga and Ge)

Using ¹⁰⁰Pd/¹⁰⁰Rh probes, perturbed angular correlation measurements were performed to study Pd-related defects in Si as a function of dopant concentration and dopant type. Pd-vacancy and Pd-B complexes were identified by their characteristic electric field gradients in highly doped n- and p-type Si, respectively. Both pairs exhibited a T^3/2 temperature dependence of their electric field gradients.     

Electronic properties of HfXY intermetallic compounds (X = Si, Ge; Y = S, Se, Te)

Muonium, with a positive muon as the nucleus is considered a light isotope of hydrogen displaying a close chemical analogy to this atom. It offers a unique opportunity to study the behaviour of hydrogen in diamond at very low concentrations. The mass difference, however, implies that dynamical effects will be distinct. The bond centred muonium (Mu _BC ) state in diamond is easily observed and there is a very good correlation between theoretical and experimental hyperfine parameters (Schneider et al., Phys. Rev. Lett. 71(4):557–560, 1993). Curiously, despite its predicted stability, the bond centred hydrogen state has not yet been observed in diamond. Following the discovery of hydrogen dopant states in certain wide band gap metal oxides, and the possibility of hydrogen related molecular dopants in diamond, the study of hydrogen in diamond is important. Although it is evident from its hyperfine parameters that Mu _BC is not a shallow donor, the question still arises as to where the Mu _BC state in diamond might lie in the band gap. Accordingly, measurements of the high temperature stability of Mu _BC have been performed in a search for its possible ionization. The results are consistent with such an ionization, as the disappearance of Mu _BC polarisation (setting in near 1000 K) is correlated with the slight increase in the population of the diamagnetic μ⁺ species.