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Structural Properties of Some Alkali Metal Hydrides at High Temperature and Pressure

100%

Thakre V. , Singh S.

tom 133

nr 1

186-193

In this paper we have developed a realistic interaction potential model to study the high pressure phase transition of ionic alkali-metal compounds KH and NaH, having B₁ structure at room temperature. We have theoretically investigated phase transition pressures and volume collapses of KH and NaH at high temperatures, and found results well suited with available experimental data. The elastic constants and their pressure derivatives are reported first time. The thermodynamical properties of B₁ phase of KH and NaH are also predicted. The inclusion of temperature effect in TBIP makes the present model realistic and suitable for theoretical high-pressure studies.

Energetics, electronic structure, and structure stability of the calcium alloying Mg17Al12 phase from first principles calculations

84%

Zhou D. W. , Peng P. , Liu J. S.

Materials Science Poland

2007

tom Vol. 25, No. 1

145--153

The energetics and electronic structure of the Ca alloying Mg 17Al12 phase have been calculated using a first principles pseudopotential plane-wave method based on the density functional theory. According to the calculation results, the negative heat of formation and the cohesive energy of (Mg17-xCax)Al12 (x = 0. 1, 4, 12) gradually increase when the Mg atoms at the I, II, III positions of the Mg17Al12 phase are substituted with Ca, which indicates that the alloying ability of (Mg17-xCax)A,)Al12 with the replacement of Ca for Mg(III) atoms is the strongest among the three substitutions and (Mg5Ca12)Al12 formed in this manner has the highest structural stability. After comparing the densities of states (DOS) for (Mg17-xCax)Al12 (x = 0. 1, 4, 12), it is found that the increase in the structural stability of Mg 17Al12 alloyed by Ca attributes to an increase in the bonding electron numbers at energy levels below the Fermi level, which mainly originates from the contribution of the valence electron numbers of Al (p) and Ca (s) orbitals.