Domain formation and phase transitions in the wurtzite-based heterovalent ternaries: a Landau theory analysis

Abstract

Characterizing the crystalline disorder properties of heterovalent ternary semiconductors continues to challenge solid-state theory. Here, a Landau theory is developed for the wurtzite-based ternary semiconductor ZnSnN 2 . It is shown that the symmetry properties of two nearly co-stable phases, with space groups Pmc2 1 and Pbn2 1 , imply that a reconstructive phase transition is the source of crystal structure disorder via a mixture of phase domains. The site exchange defect, which consists of two adjacent antisite defects, is identified as the nucleation mechanism of the transition. A Landau potential based on the spacegroup symmetries of the Pmc2 1 and Pbn2 1 phases is constructed from the online databases in the ISOTROPY software suite and this potential is consistent with a system that undergoes a paraelectric to antiferroelectric phase transition. It is hypothesized that the low-temperature Pbn2 1 phase is antiferroelectric within the c-axis basal plane. The dipole arrangements within the Pbn2 1 basal plane yield a nonpolar spontaneous polarization and the electrical susceptibility derived from the Landau potential exhibits a singularity at the Né el temperature characteristic of antiferroelectric behavior. These results inform the study of disorder in the broad class of heterovalent ternary semiconductors, including those based on the zincblende structure, and open the door to the application of the ternaries in new technology spaces.

Symmetry relations in wurtzite nitrides and oxide nitrides and the curious case of Pmc21

“…They are, however, crucially important for a proper understanding of symmetry relations, and we would like to showcase this for the case of Pmc2 1 , a space group that has been postulated for ternary nitrides for a long time (e.g. Baur & McLarnan, 1982;Quayle et al, 2015;Quayle, 2020).…”

A discussion on `Domain formation and phase transitions in the wurtzite-based heterovalent ternaries: a Landau theory analysis'

“…The symmetry relation upon which the Landau theory of Quayle (2020) is based is between the Pmc2 1 structure and the -Pna2 1 structure; therefore, the derived order parameter describes this phase transition. Quayle (2020) however describes the transition, and order parameter, as between the Pmc2 1 structure and the -Pna2 1 structure.…”

“…The analysis is formally correct however if we realize that the subgroup phase is -Pna2 1 not -Pna2 1 . Also, it can be argued that both Pna2 1 phases are antiferroelectric, using the methodology in Quayle (2020), so that aspect of the analysis remains unchanged.…”

“…The formal analysis ends at the transition from Pmc2 1 to -Pna2 1 . To find a logical path from the -Pna2 1 phase to -Pna2 1 we must depart from group theory arguments and note that if a ternary nitride can transition from AAAA basal plane ordering (Pmc2 1 ) to AABB ordering (-Pna2 1 ) by way of a mechanism similar to the one described in Quayle (2020), then it is plausible that it can also transition further to the more energetically favourable ABAB ordering of -Pna2 1 .…”

“…Although it is nominally a ternary compound, no clear crystallographic evidence for cation ordering has been observed so far. An attempt to elucidate this discrepancy [Quayle (2020). Acta Cryst.…”