Phase transformation of AlAs to NiAs structure at high pressure

Structural, Mechanical, Anisotropic, and Thermal Properties of AlAs in oC12 and hP6 Phases under Pressure

The structural, mechanical, anisotropic, and thermal properties of oC12-AlAs and hP6-AlAs under pressure have been investigated by employing first-principles calculations based on density functional theory. The elastic constants, bulk modulus, shear modulus, Young’s modulus, B/G ratio, and Poisson’s ratio for oC12-AlAs and hP6-AlAs have been systematically investigated. The results show that oC12-AlAs and hP6-AlAs are mechanically stable within the considered pressure. Through the study of lattice constants (a, b, and c) with pressure, we find that the incompressibility of oC12-AlAs and hP6-AlAs is the largest along the c-axis. At 0 GPa, the bulk modulus B of oC12-AlAs, hP6-AlAs, and diamond-AlAs are 76 GPa, 75 GPa, and 74 Gpa, respectively, indicating that oC12-AlAs and hP6-AlAs have a better capability of resistance to volume than diamond-AlAs. The pressure of transition from brittleness to ductility for oC12-AlAs and hP6-AlAs are 1.21 GPa and 2.11 GPa, respectively. The anisotropy of Young’s modulus shows that oC12-AlAs and hP6-AlAs have greater isotropy than diamond-AlAs. To obtain the thermodynamic properties of oC12-AlAs and hP6-AlAs, the sound velocities, Debye temperature, and minimum thermal conductivity at considered pressure were investigated systematically. At ambient pressure, oC12-AlAs (463 K) and hP6-AlAs (471 K) have a higher Debye temperature than diamond-AlAs (433 K). At T = 300 K, hP6-AlAs (0.822 W/cm·K⁻¹) has the best thermal conductivity of the three phases, and oC12-AlAs (0.809 W/cm·K⁻¹) is much close to diamond-AlAs (0.813 W/cm·K⁻¹).

Electrical transport properties of AlAs under compression: reversible boundary effect

Herein, we report on the intriguing electrical transport properties of compressed AlAs. The relative permittivity and the resistances of both the grain and bulk boundaries vary abnormally at ∼10.9 GPa, accompanied by the cubic-hexagonal structural transition of AlAs. With further compression, the boundary effect becomes undistinguished, and subsequently, the electrical transport mechanism converts from boundary- to bulk-dominated, which gives rise to a significant reduction in the total resistance of AlAs. After being quenched to ambient pressure, resistances recover to the initial values followed by the re-emergence of the boundary effect. Eg decreases with pressure and its pressure dependence changes at ∼14.0 GPa, which rationalizes the anomalous variation of the electrical transport properties. The experimental results indicate that the boundary effect can be modulated by compression and increases the resistance difference between the two states. This opens up a new possible basis for optimizing the performance of AlAs-based applications, including multilevel phase-change memories.