# A First-Principles Study of Epitaxial Strain as a Method of B4 to BCT Stabilisation in ZnO, ZnS, and CdS

Density-functional-theory calculations have been used to examine stabilization of the low density BCT polymorph by epitaxial strain. The relative energies of B4 and BCT polymorphs were calculated for ZnO, ZnS, and CdS, as a function of epitaxial strain, for a B4[0001]||BCT[010]/B4[1-210]||BCT[001] correspondence. The phase stability is mapped in $${u,v}$$ parameter space and the challenge of identifying a suitable epitaxial support to direct growth of the BCT phase is discussed. For ZnS, ZnSe, ZnTe, CdS, and CdSe, the optimized “BCT” geometry is orthorhombically distorted, in contrast to the tetragonal lattices of ZnO, CdO, and InN. This orthorhombic distortion is associated with a rotation of the four-membered rings in the BCT structure, and is enhanced in ZnO, ZnS, and CdS under epitaxial strain.