Raman spectroscopic study of ceramic Sr2Bi4Ti5O18

Raman spectra of ceramic Sr2Bi4Ti5O18 （SBTi5） are reported to consist of four different Raman bands. Temperature-dependent spectra reveal the relationship between the lattice vibration and the material＇s structure. There appears a relatively large change in structure of the material at about 273K, The anharmonic potential of the material has a great influence on its phonon mode full width at half maximum （FWHM）, which can be expressed by a function of temperature. Theoretical fittings of the FWHMs for the two modes at around 312 cm^-1 and 464cm^-1 indicate that the latter phonon mode is more anharmonic than the former one.     

Epitaxial growth and transport properties of compressively-strained Ba2IrO4 films

Ba₂IrO₄ is a sister compound of the widely investigated Sr₂IrO₄ and has no IrO₆ octahedral rotation nor net canted antiferromagnetic moment, thus it acts as a system more similar to the high-T_c cuprate. In this work, we synthesize the Ba₂IrO₄ epitaxial films by reactive molecular beam epitaxy and study their crystalline structure and transport properties under biaxial compressive strain. High resolution scanning transmission electron microscopy and x-ray diffraction confirm the high quality of films with partial strain relaxation. Under compressive epitaxial strain, the Ba₂IrO₄ exhibits the strain-driven enhancement of the conductivity, consistent with the band gap narrowing and the stronger hybridization of Ir-t_2g and O-2p orbitals predicted in the first-principles calculations.