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Gas-phase nitrogenation of CoTiSn compound with the MgAgAs-type structure has been examined by means of x-ray diffraction (XRD) and x-ray absorption fine structure (XAFS). The XRD suggests that the nitrogenation product is composed of the corresponding Cu2MnAl-type compound with expanded unit-cell volume comparable to that of Co2TiSn and subtle trace of Ti6Sn5 and Sn. Whereas the x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) spectra for the Ti, Co and Sn K-edges clearly indicate the coexistence of TiN and Co1+yTiSn phases in the product. It is also revealed that more Co atoms than expected from the chemical formulas are introduced into the vacancy site of the MgAgAs structure in Co1+yTiSn with 0≤y≤0.4.

By performing isobaric-isothermal molecular dynamics simulations for Ti we have obtained the result that the `modified embedded atom method' potential creates stable structures different from the hcp structure, with a non-ideal c/a ratio that is experimentally stable. The hcp-to-bcc transformation at high temperature is reproduced. However, attempts to make the hcp structure the ground state structure, by adjusting the many-body screening function or by taking the second-nearest neighbour interactions into account, have been unsuccessful. Structural stabilities of other hcp metals have also been examined.

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