Theoretical investigation on thermophysical, mechanical, and ultrasonic properties of $\rm NbN$ layers deposited on $\rm MgO(001)$ substrates at high temperature

In the present paper, we calculated the elastic, mechanical, and thermophysical properties of $\rm NbN/\rm MgO(001)$ layers in the temperature range $600$–$900^{\circ}$C using higher order elastic constants. With two fundamental factors, nearest-neighbour distance as well as hardness parameter, the second and third order elastic constants are estimated using the Born–Mayer potential approaches. The computed values of second order elastic constant are used to calculate Young modulus, thermal conductivity, Zener anisotropy, bulk modulus, thermal energy density, shear modulus as well as Poisson ratio in order to assess the thermal and mechanical properties of $\rm NbN/\rm MgO(001)$ layers. Additionally, the second order elastic constant is also used to calculate the wave velocities for shear and longitudinal modes of propagation along crystalline orientations $[100]{,}~[110]{,}~[111]{.}$ Temperature dependent Debye average velocity, hardness, and ultrasonic Grüneisen parameters are evaluated. The fracture/toughness $B/G$ ratio in the current investigation is more than $1.75$, indicating that the $\rm NbN/\rm MgO(001)$ nanostructured layer is ductile in nature in this temperature range. The selected materials are fully satisfying the Born mechanical stability requirement. The time required for thermal relaxation is calculated and how ultrasonic waves are attenuated by thermo-elastic relaxation and phonon–phonon interaction mechanisms. The findings with other well-known physical features are helpful for industrial applications.