Correlation effects and phonon modes softening with doping in Ba1-xKxBiO3

摘要

Monoclinic crystal structure of the undoped BaBiO3 can be described as acubic perovskite distorted by a frozen breathing and tilting phonon modes ofBiO6 octahedra. The phonon mode softening is experimentally observed [M. Bradenet al., Europhysics Letters (EPL) 34, 531 (1996)] in Ba1-xKxBiO3 throughpotassium doping followed by a transition into an ideal cubic perovskitestructure at x = 0.37 close to the appearance of superconductivity. In ourprevious paper [D. Korotin et al., Journal of Physics: Condensed Matter 24,415603 (2012)] we demonstrated that it is necessary to take into accountcorrelation effects by DFT+U method in Wannier functions basis to obtain a goodagreement between the calculated and experimental values of crystal structuredistortion and energy gap in BaBiO3. In the present work with the same methodwe calculated the breathing mode phonon frequencies as a function of potassiumdoping level in Ba1-xKxBiO3. Obtained frequencies are in a good agreement withexperimental values and the breathing mode softening with doping effect isreproduced while calculations without consideration of correlation effectsfailed to do so. We shown that the cubic crystal structure becomes stable at x= 0.30 in agreement with the experimental transition to cubic perovskite at x =0.37. The possible connections between the correlation effects, phonon modesoftening, and superconductivity in Ba1-xKxBiO3 are discussed.