Electronic structure, phonons, and thermal properties of ScN, ZrN, and HfN: A first-principles study

Abstract

With a motivation to understand microscopic aspects of ScN, ZrN, and HfN relevant to the thermoelectric properties of nitride metal/semiconductor superlattices, we determine their electronic structure, vibrational spectra and thermal properties using first-principles calculations based on density functional theory with a generalized gradient approximation of the exchange correlation energy. We find a large energy gap in the phonon dispersions of metallic ZrN and HfN, but a gapless phonon spectrum for ScN spanning the same energy range, this suggests that a reduced thermal conductivity, suitable for thermoelectric applications, should arise in superlattices made with ScN and ZrN or ScN and HfN. To obtain an electronic energy band gap of ScN comparable to experiment, we use a Hubbard correction with a parameter U ͑=3.5 eV͒. Anomalies in the acoustic branches of the phonon dispersion of ZrN and HfN, manifested as dips in the bands, can be understood through the nesting of Fermi surface determined from our calculations. To connect with transport properties, we have determined effective masses of ScN and determined their dependence on the U parameter. Using the relaxation time approximation in the Boltzmann transport theory, we estimate the temperature dependence of the lattice thermal conductivity and discuss the chemical trends among these nitrides.

Phase stability of ScN-based solid solutions for thermoelectric applications from first-principles calculations

“…This is qualitatively in line with the calculations of the dilute case in Ref. 51. It can be understood since the extra delectrons with t2g symmetry from Ti, Zr, and Hf has to occupy gradually higher energies of the empty Sc 3d t2g state when their concentrations in the alloys increase.…”

“…The tendency of mixing of TiN/ZrN/HfN and ScN should also be kept in mind when designing superlattices between them as the transformation of these superlattices to a metallic solid solution would destroy their thermoelectric performance completely. 51 A second strategy is using inclusions to reduce lattice thermal conductivity. The results indicate that we can use Y, La, Gd, Al, Ga, In, P, As, and Sb, since these systems have phase separation tendency and they tend to have isostructural, possibly semi-coherent, interfaces after the decomposition which should have minor effects on carrier mobility.…”

Hot carrier solar cell absorbers: materials, mechanisms and nanostructures

“…30,31 However the IVA nitrides of Hafnium and Zirconium have large predicted and measured phononic gaps, 30 both bigger than their acoustic phonon energies. The phonon gap for TaN is reasonable but not as large as its acoustic phonon energy.…”

FP-LAPW investigation of electronic, magnetic, elastic and thermal properties of Fe-doped zirconium nitride

“…ZrN is also a useful candidate for Josephson junctions as per the earlier works done by K. Schwarz et al 9 in the year 1985. B. Saha et al 10 studied electronic structure and thermal properties of ScN, ZrN and HfN using fist principles study. Zhigang Wu et al 11 worked on elasticity and electronic structure of transition metal nitrides.…”