CALCIUM-ION SELECTIVE SITE OCCUPATION AT RUDDLESDEN-POPPER-TYPE FAULTS AND THE RESULTANT DIELECTRIC-PROPERTIES OF A-SITE-EXCESS STRONTIUM CALCIUM TITANATE CERAMICS

The microstructure and dielectric properties of A-site-excess and stoi chiometric-composition strontium calcium titanate ((Sr,Ca)TiO3) cerami cs were investigated in the present study. Ruddlesden-Popper-type plan ar faults in A-site-excess specimens were observed using high-resoluti on scanning transmission electron microscopy (HR-STEM). STEM microchem ical analysis, calculation of the high-resolution image using a multis lice method, and structural-energy calculation further revealed that c alcium ions selectively occupied the cation sites of the faults. An ob served shift of the peak dielectric constant to low temperature and th e expansion of the lattice parameter of the A-site-excess specimen wer e attributed to the selective occupation of the cation sites of the pl anar faults by calcium ions.