Spectroscopic investigation on the electronic structure of a 5d band insulator SrHfO3 in proximity to ferroelectric instability: Comparison with SrTiO3 and SrZrO3

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.