No abstract

The effects of magnesium and niobium substitution for titanium on the microwave dielectric properties of Ba 3.75 Nd 9.5 Ti 18Àz (Mg 1/3 Nb 2/3 ) z O 54 (0 £ z £ 3) ceramics were studied. The temperature coefficient of resonant frequency (s f ) decreased from about +60 ppm/°C to +17 ppm/°C when z £ 1. Excellent quality factor (Qf = 7300 GHz) as well as high dielectric constant (e r = 80.96) were obtained. For z ‡ 1.5, Nd 2 (Ti,Mg,Nb) 2 O 7 secondary phase appeared which would obviously influence the microwave dielectric properties. As z varied from 0 to 3, matrix grain size degraded which would obviously deteriorate the microwave dielectric properties by conducting more pores, especially the Qf value. The s f value was found to be related to b-site bond valence (V B-O ) and unit cell volume (V m ). Average ionic polarizability (a D ) and relative density evidently influenced the dielectric constant.

Ferroelectric thin film capacitors have attracted increasing attention because of their high energy storage density and fast charge–discharge speed, but less attention has been paid to the realization of flexible capacitors for wearable electronics and power systems. In this work, flexible xMn‐BiMg0.5Ti0.7O3 (xMn‐BMT0.7) thin film capacitors with ultrahigh energy storage density and good stability are deposited on mica substrate. The introduction of excess TiO2 with an amorphous structure contributes to the forming of the polar nano regions, resulting in the reduced ferroelectric hysteresis. In order to further improve the energy storage performance, Mn doping increases the polarization by regulating chemical pressure in the lattices and inhibits the valence change of Ti4+. Especially in the 1.5% Mn‐BMT0.7 film capacitor, an ultrahigh energy storage density of 124 J cm‐3 and an outstanding efficiency of 77% are obtained, which is one of the best energy storage performances recorded for ferroelectric capacitors. In addition, the flexible ferroelectric film capacitor also exhibits good thermal stability (25–200 °C), high frequency reliability (500 Hz–10 kHz), excellent electrical (108 cycles), and mechanical (104 cycles) fatigue properties. This work is expected to pave the way for the application of BMT‐based thin film capacitors in flexible energy storage systems.