First-principles study of the properties of Pmn21-B1-xAlxN

The structural, mechanical, elastic anisotropic, thermodynamic and optoelectronic properties of Pmn2(1)-B1-xAlxN are investigated using density functional theory (DFT) calculations. For BN and AlN, the lattice parameters, elastic constants and elastic modulus are found to be in agreement with others' theoretical data. The absence of any imaginary phonon frequencies in the entire Brillouin zone confirms that Pmn2(1)-B1-xAlxN alloys are dynamically stable. The vibration modes transfer from high frequency to low frequency with the increase of the component Al. All of Pmn2(1)-B1-xAlxN (x = 0, 0.25, 0.50, 0.75, 1) behave in a brittle manner. Ternary BAlN alloys are more anisotropic than BN and AlN. The Debye temperature decreases with the increase of the component Al. At temperatures below 2000 K, the heat capacity of Pmn2(1)-B1-xAlxN increases with the increase of the component Al. For B0.5Al0.5N, below the Fermi level, B p contributes more than Al p, whereas above the Fermi level, Al p contributes more than B p. With the increase of composition Al, B-N interactions become weaker and Al-N interactions become stronger, and the dielectric function, absorption and Raman intensity drift from high-frequency to low-frequency.