Nonreversible Transition from the Hexagonal to Wurtzite Phase of Boron Nitride

Wurtzite Boron Nitride (wBN) is a wide band gap BN polymorph with unique mechanical properties such as hardness and stiffness. Initially synthesized in 1963 by transforming hexagonal BN (hBN) under high temperature and pressure conditions, wBN can now be stabilized at atmospheric pressure to obtain high-quality samples. Our first-principles study investigates the electronic, vibrational, and optical properties of wBN across a broad range of pressures. We account for the electron-hole interaction in the optical response, revealing that this effect is crucial to interpret the available experimental spectra. We also calculate the coupling between excitons and phonons and provide a phonon-assisted emission spectrum centered around 6.02 eV. Our results hold significant importance for applying wBN as a dielectric material in BN-based technologies, especially in optoelectronics and harsh environments. We also expect our prediction to be verified in the future, and it could aid in identifying wBN through cathodoluminescence experiments. We present an infrared reflectance and transmission study of a pressure-induced phase transition of boron nitride from the hexagonal layered structure to the wurtzite phase. This allows the infrared-active optical phonons and the dielectric properties of the cold-pressed wurtzite boron nitride sample to be studied over the whole range of pressures. Experimental permittivity values of ε0 = 6.65 ± 0.03 and ε∞ = 4.50 ± 0.05 are determined from fits to the reflectance spectra at ambient pressure. Accurate refractive index values in the mid-infrared and visible–ultraviolet regions are evaluated from the interference patterns. Contrary to the h-BN case, the refractive index of w-BN decreases slightly with pressure on account of the much lower compressibility of the close-packed structure. The pressure coefficients for the longitudinal optical and transverse optical modes are determined, and an overall good agreement with ab initio calculations is found. If you are looking for high quality, high purity and cost-effective Wurtzite Boron Nitride, or if you require the latest price of Wurtzite Boron Nitride, please feel free to email contact mis-asia.