Descriptors for Electron and Hole Charge Carriers in Metal Oxides

Abstract

Metal oxides can act as insulators, semiconductors or metals depending on their chemical composition and crystal structure. Metal oxide semiconductors, which support equilibrium populations of electron and hole charge carriers, have widespread applications including batteries, solar cells, and display technologies. It is often dicult to predict in advance whether these materials will exhibit localized or delocalized charge carriers upon oxidation or reduction. We combine data from first-principles calculations of the electronic structure and dielectric response of 214 metal oxides to predict the energetic driving force for carrier localization and transport. We assess descriptors based on the carrier e↵ective mass, static polaron binding energy, and Fröhlich electron-phonon coupling. Numerical analysis allows us to assign p and n type transport of a metal oxide to three classes: (i) band transport with high mobility; (ii) small polaron transport with low mobility; and (iii) intermediate behaviour. The results of this classification agree with observations regarding carrier dynamics and lifetimes and are used to predict 10 candidate p-type oxides.

Anharmonic lattice dynamics of superionic lithium nitride

“…Phonon or vibrational density-of-states data have also been used to construct a range of cheap-to-compute descriptors for various properties of fast-ion conductors, including for ionic conductivity, activation energy, and electrochemical stability window [20,21]. Computationally cheap descriptors of specific properties are increasingly used in high-throughput materials discovery, where data from electronic-structure methods are combined with data-mining techniques to screen large numbers of materials to identify candidates with, hopefully, desirable properties [22,23,24,25]. The Debye frequency, obtained by speed-of-sound measurements, and the mobileion phonon band-centre, ω av , calculated from density functional theory (DFT) or from inelastic neutron scattering data, have previously been proposed as descriptors for ionic conductivity and activation energy, respectively, within individual solid electrolyte families [26,27,20].…”

Low Electronic Conductivity of Li7La3Zr2O12 (LLZO) Solid Electrolytes from First Principles

“…This large discrepancy between ionic ( ion ) and high frequency ( ∞ = 2.07) dielectric response implies large electron-phonon coupling. 44 Using these data to calculate maximum room-temperature carrier mobility (considering both at the VBM and CBM) yields a value of of 0.06 cm 2 V −1 s −1 .…”

“…43 The inputs for this calculation are the dielectric constant of the solid electrolyte, Born effective charges, a characteristic phonon frequency and charge-carrier effective masses: again, these are all calculable using first-principles methods. 44 We now turn to the application of this theoretical framework, illustrated schematically in Fig. 1, to calculate the electronic conductivity of LLZO.…”

Computationally Driven Discovery of Layered Quinary Oxychalcogenides: Potential p-Type Transparent Conductors?

“…Additionally, the polaronic binding energy of holes can be calculated for BaSc and SrSc, giving rise to values of 0.04 eV and 0.08 eV, respectively, within the ab plane, categorizing them as type II compounds as per the convention defined by Davies et al. 69 It is clear that BaSc will be a better p -type conductor than SrSc, although while these values are slightly above any room-temperature excitation (∼0.03 eV at k B T at 300 K) it can be expected that excitation could occur from photons with wavelengths greater than mid-infrared (IR). 70 …”