Stability and phonons of KTaO3

KTaO3 was investigated using density functional methods. These local-density approximation calculations correctly show the absence of a ferroelectric instability in this compound. Phonon frequencies and bulk properties in good agreement with existing measurements are obtained. A highly anharmonic low-frequency mode corresponding to the observed incipient ferroelectric behavior is identified. The electronic structure shows strong transition metal oxygen covalency as in known ferroelectric perovskites. As expected properties similarity with KNbO3. The absence of ferroelectricity in KTaO3 is due to the extreme sensitivity of the soft mode to the covalency and the slight chemical differences of Nh and Ta, particularly the higher d binding energy in Nb.