Potassium Titanyl Phosphate Z- And Y-Cut Surfaces From Density-Functional Theory

While potassium titanyl phosphate (KTP) is widely used for various optics applications, essentially nothing is known about its surfaces and electronic properties. Here the ground-state atomic structures of KTP [001] and [010] surfaces, frequently termed Z and Y cuts, respectively, have been determined using ground-state density-functional theory total-energy calculations. The calculated surface phase diagrams in dependence on the chemical potentials of the materials constituents show several stable nonstoichiometric terminations. A tendency to form oxygen-rich surfaces is observed. The Z(+) and Z(-) surfaces, discriminated by oppositely orientated internal electric fields, are found to differ with respect to their stoichiometry and structure. Occupied O-derived and in some cases unoccupied Ti-derived surface states appear in the lower and upper part of the bulk band gap, respectively.