Spectroscopic investigation on the electronic structure of a 5d band insulator in proximity to ferroelectric instability: Comparison with and

We investigated the high-energy electronic structure of a 5d perovskite SrHfO3 by using optical spectroscopy and O 1s x-ray absorption spectroscopy. From the combined spectra the values of electronic structure parameters are estimated properly. In particular, the crystal field splitting energy, which is closely associated with the p–d hybridization strength, is as high as ∼5 eV, and the Sr 4d bands appear to be strongly mixed with the Hf 5d bands. These findings are discussed in relation to a possible ferroelectric instability in SrHfO3, and are compared with electronic properties of similar compounds, 3d SrTiO3 and 4d SrZrO3.