Fermi Level Instability as a Way to Tailor Properties of La3Te4

TL;DR

This paper reveals that Fermi level instability in La3Te4 leads to spontaneous defect formation, enabling control over its electronic properties and phase transitions through synthesis conditions.

Contribution

It demonstrates that Fermi-level instability causes off-stoichiometry and self-doping in La3Te4, offering a new approach to tailor material properties.

Findings

La vacancies form spontaneously in La3Te4

Fermi-level instability drives off-stoichiometry

Controlling synthesis can induce metal-insulator transitions

Abstract

Traditionally, the formation of off-stoichiometric compounds is believed to be the growth effect rather than the intrinsic tendency of the system. However, here, using the example of La3Te4, we demonstrate that in n-type gapped metals having a large internal gap between principal band edges and the Fermi level inside of the principal conduction band, Fermi-level instability can develop, resulting in a reduction of formation energy for acceptor defects. Specifically, La vacancies in La3Te4 form spontaneously to produce the acceptor states and remove a fraction of free carriers from the principal conduction band via electron-hole recombination. Such a unique self-doping mechanism allows to stabilize a range of off-stoichiometric La3-xTe4 compounds, which have different electronic properties. Moreover, we thus show how controlling synthesis conditions can be used as a knob to reach the target functionality, including controllable metal-to-insulator transition.