TY - JOUR
T1 - Preferential stability of the d-BCT phase in ZnO thin films
AU - Morgan, Benjamin
PY - 2009/9/21
Y1 - 2009/9/21
N2 - Stoichiometric B4 thin films have formally divergent surface energies, which arise from the intrinsic dipole of the unit cell. Previous density functional theory studies have predicted that below a critical thickness this results in relaxation to the nonpolar planar h-MgO structure. The calculations presented here demonstrate that h-MgO-structured ZnO thin films are themselves unstable with respect to further relaxation to the d-BCT structure, which restores near-tetrahedral local coordination while minimizing the surface dipole. Although the B4→h-MgO relaxation is disfavored for slabs thicker than 20 layers, d-BCT is predicted to be the favored polymorph for slabs up to 54 layers. Nudged elastic band calculations and vibrational analysis indicate that the h-MgO→d-BCT relaxation is spontaneous at nonzero temperatures.
AB - Stoichiometric B4 thin films have formally divergent surface energies, which arise from the intrinsic dipole of the unit cell. Previous density functional theory studies have predicted that below a critical thickness this results in relaxation to the nonpolar planar h-MgO structure. The calculations presented here demonstrate that h-MgO-structured ZnO thin films are themselves unstable with respect to further relaxation to the d-BCT structure, which restores near-tetrahedral local coordination while minimizing the surface dipole. Although the B4→h-MgO relaxation is disfavored for slabs thicker than 20 layers, d-BCT is predicted to be the favored polymorph for slabs up to 54 layers. Nudged elastic band calculations and vibrational analysis indicate that the h-MgO→d-BCT relaxation is spontaneous at nonzero temperatures.
UR - http://dx.doi.org/10.1103/PhysRevB.80.174105
U2 - 10.1103/PhysRevB.80.174105
DO - 10.1103/PhysRevB.80.174105
M3 - Article
VL - 80
JO - Physical Review B : Condensed Matter and Materials Physics
JF - Physical Review B : Condensed Matter and Materials Physics
SN - 1098-0121
IS - 17
ER -