Polar Nanoregions and Dielectric Properties of BaTiO3‐Based Y5V Multilayer Ceramic Capacitors

Abstract

Commercial EIA‐Y5V base‐metal‐electrode multilayer ceramic capacitors (BME‐MLCCs) made of (CaO+ZrO2)‐doped BaTiO3 are analyzed for the microstructure and investigated for its relation to dielectric properties. The characteristic diffuse scattering (DS) intensities observed in BaTiO3 ceramics and the featureless “solid‐solution” grains in Y5V capacitor chips are originated from multiple Ti sites in the dynamic BaTiO3 structure. The pseudo‐cubic (PC)‐grains retaining the overall cubic (C‐) symmetry metastably at room temperature are embedded with polar nanoregions (PNRs) in the ferroelectric (FE) tetragonal (T‐), and rhombohedral (R‐) phases, as revealed by high‐resolution transmission electron microscopy (HRTEM). The presence of PNRs contributes effectively to large relative permittivity εr ≈ 13 200 at 25°C. The FE T‐domains grow from within PC‐grains at the expense of embedded PNRs after prolonged annealing by extending “oxidizing firing” at 950°C in pO2 = 10−7 atm. These domains contain less Zr with otherwise homogeneously distributed solutes in PNR‐dispersed PC‐grains. Although preserving the relaxors characteristics, εr is reduced to ~11 000 after 12 h, and then to ~9000 after 24 h annealing. The reduction in εr is attributed to the annealing‐induced FE T‐domains grown at the expense of PNRs in PC‐grains. The Vögel–Fulcher analysis indicates that Y5V ceramics are in the relaxor FE category, containing PNRs derived from polarization frustration.