The influence of transition metals (TMs) on the hydriding/dedydriding critical point of NaAlH4 has been studied using the chemical potential method. The theoretical results predict that, if the reaction system reaches equilibrium, most of the TM additives significantly increase its hydriding/dedydriding critical point in the sequence Pd>Co>Zr>Ni>Nb>Hf>Ti>Mn>Fe>V>Cu>Cr and therefore have destabilizing effects on NaAlH4 in the same sequence. Experimentally, the isothermal dehydriding kinetics of NaAlH4 is studied only with Fe, Ti, and FeTi additives. The experimental results show that the destabilizing effect of Fe and Ti additives with coarse particles is very low while more effective destabilizing ability is achieved with fine FeTi particles. These experimental results suggest that the predicted destabilizing effect of TM additive is hindered kinetically due to the coarse particles of additives, and therefore experimental verification of the destabilizing effect of TMs should be performed with nanosized particles.

Zr mono-doped and (Zr,N) co-doped ZnO are investigated by the first-principles calculations. It is found that Zr prefers to substitute Zn site under most growth conditions. The passive (N-Zr-N) complexes create a fully occupied impurity band above the valence-band maximum (VBM) of ZnO, which helps p-type conductivity by reducing the ionization energy, consistent with a new approach to overcome the doping asymmetry [Y.F.Yan, J.B.Li, S.H.Wei, and M.M. Al-Jassim, Phys. Rev. Lett. 98 (2007) 135506]. In comparison with (Ga,N) co-doping, (Zr,N) is found to be probably better dopants to push p-type conductivity in ZnO through the new approach with easier formation of the passive impurity band.

The electronic and magnetic properties of Mn doping at either cation sites in the class of Ⅰ-Ⅲ-Ⅵ2 chalcopyrites are studied by first-principles calculation. It is found that Mn doping at the Ⅲ site provides holes and stabilizes the ferromagnetic interaction between neutral Mn defects; the neutral MnoCu also stabilizes the ferromagnetism, although it provides electrons to the conduction band, instead of holes. The ferromagnetic stability is generally weaker when the cation or the anion becomes heavier in these chalcopyrites, i.e., along the sequences CuAlS2→CuGaS2→CuInS2 and CuGaS2→CuGaSe2→CuGaTe2. Interestingly, CuAlO2 in the chalcopyrite structure is predicted to have lower FM energy than CuAlS2 despite its lighter anion and shorter bonds. In general, Ⅲ site substitution gives stabler ferromagnetism than Cu substitution. Thus, the preferred growth conditions are Cu-rich and Ⅲ-poor, which maximize MnⅢ replacement. In n-type samples, when MnⅢ is negatively charged, the antiferromagnetic coupling is preferred. In p-type samples, the ground state of positively charged Mn+Cu is also antiferromagnetism. The main feature of the calculated electronic properties of Mn defect at either Cu or Ⅲ site is explained using a simple picture of dangling bond hybride and crystal-field resonance.

The influence of defect charge state on the magnetism of Cu doped ZnO as well as the Cu defects clustering have been investigated by the first-principles calculations. We demonstrate that p-type ZnO:Cu could have ferromagnetic (FM) property, but n-type ZnO:Cu would not have local magnetic moment. Furthermore, the neutral substitutive Cu defects are found to be favorable in clustering, which maintains the FM ordering.

The recently reported room-temperature ferromagnetism in Cd1-xMnxGeP2 was investigated for x＝1.0,0.5, and 0.25 by the local density first-principles full-potential linearized augmented plane wave（FLAPW）and DMOL3 methods within both local-density approximation（LDA）and generalized gradient approximation (GGA). We find that the total energy of the antiferromagnetic（AFM）state is lower than the corresponding ferromagnetic (FM) state for all x studied. The GGA gives a better description of magnetic properties than LDA mainly due to its better prediction of structure, particularly for high Mn concentrations. The total spin moment of Cd1-xMnxGeP2 is～5.0µB per Mn atom. The FM alignment between Mn and Pincreases the total energy of the Mn-Mn FM coupling and makes the AFM ordering preferable.