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We report on the electronic, thermal, and elastic properties of the layered ternary, Ti 2 SC. Resistivity, Hall effect, and magnetoresistance were measured as a function of temperature between 2 and 300 K and at fields up to 9 T. The Hall coefficient is negative and roughly temperature independent. The transport results were analyzed within a two-band framework, with electrons as the dominant charge carrier. The room-temperature thermal conductivity ͑Ϸ60 W / m K͒ is the highest of any MAX phase measured to date, with a substantial phonon contribution. The specific heat was measured from 2 to 300 K, yielding a Debye temperature of 765 K and in agreement with the Debye temperature of 745 K found from ultrasonic time-of-flight measurements. Young's, shear, and bulk moduli from the latter measurements were 290, 125, and 145 GPa, respectively. The calculated values of the lattice parameters ͑a = 3.2051 Å and c = 11.2636 Å͒, and Young's, shear, and bulk moduli ͑329, 138, and 179 GPa, respectively͒, based on the results of density functional theoretical simulations, compare favorably with measurements.

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The effect of hydrogenation on the magnetic properties and crystal structure of 4f and 5f intermetallics was studied on HoNiAlH2.0, UNiAlH2.3 and UNiAlD2.1. The incorporation of hydrogen into HoNiAl leads to a decrease of the magnetic ordering temperature from 13 to 6 K, while it increases from 19 K to values in the range 90–100 K in the UNiAl–H system. The crystal lattices of all compounds are anisotropically expanded. Moreover, the crystal symmetry is lowered to orthorhombic in HoNiAlH2.0, but remains hexagonal for UNiAlH(D)x. Three different deuterium positions were found for both compounds.

In this paper, we report on the heat capacities cp of bulk polycrystalline samples of Ti2AlC, V2AlC, and Cr2AlC in the 3–260K temperature range. Given the structural and chemical similarities of these compounds it is not surprising that the cp’s and their temperature dependencies were quite similar. Nevertheless, at all temperatures the heat capacity of Cr2AlC was higher than the other two. The density of states at the Fermi level were 3.9, 7.5, and 14.6(eVunitcell)−1 for Ti2AlC, V2AlC, and Cr2AlC, respectively. The results obtained are analyzed using the Debye and Einstein model approximations for cp. Good description of cp is obtained if one assumes that nine phonon modes vibrate according to the Debye model approximation whereas the remaining 3 of 12 modes expected for M2AlC formula unit fulfill an Einstein-like phonon vibration pattern. Debye temperatures θD describing acoustic phonon and Einstein temperature θE describing optical phonon contributions have been estimated for the studied compounds. The Debye temperatures are reasonably high and fall in the range of 600–700K. A linear dependence was found between the number of d electrons along the row Ti, V, and Cr and the density of states at the Fermi level.

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