Phase Mixture and Reliability of BaTiO3-Based X7R Multilayer Ceramic Capacitors: X-Ray Diffractometry and Raman Spectroscopy

Abstract

BaTiO3‐based multilayer ceramic capacitors (MLCCs) using Ni base‐metal electrodes (BME) exhibiting EIA‐X7R dielectric behavior are represented by the characteristic microstructure of core–shell grains. In the present study, the crystalline phase contents in the mixture were determined quantitatively for two groups of experimental BME‐MLCCs, one with CaO doping and the other with (CaO+MgO) codoping by Rietveld refinement using the software package TOPAS®. X‐ray diffractometry was used for the identification of crystalline phases whose quantities were determined for cubic (C), tetragonal (T), and rhombohedral (R)–BaTiO3. Phase identification was corroborated by Raman spectroscopy where the characteristic phonon vibration modes corresponding to the C‐, T‐, and R‐phase were assigned. It is suggested that the C‐phase content, corresponding to the shell grains containing intragranular voids and the shell region of the core–shell grains, and the R‐phase content, corresponding to the modulated core region, not only determine the diffusiveness of the temperature coefficient of capacitance curve but also serve as measuring indices for evaluating the resistance of MLCC formulations against dc degradation.

Core–Shell Lead–Free Piezoelectric Ceramics: Current Status and Advanced Characterization of the Bi1/2Na1/2TiO3–SrTiO3 System

“…Table reveals that systematic structure–property relationships have been performed mostly in dielectrics. This is attributed to the implementation of core–shell BT‐based dielectrics in high‐temperature capacitors owing to their temperature‐insensitive relative permittivity. However, limited research has been performed in core–shell piezoceramics.…”

“…This approach represents a new alternative for further electromechanical properties optimization in the search of environmentally friendly piezoceramics. For instance, the possibility of increasing breakdown strengths with an engineered core–shell microstructure has already been shown, where it was pointed out that an optimum design consists of a controlled shell thickness with a low relative permittivity, high insulation resistance, and density …”

“…36,38,[135][136][137] Figure 2 depicts the large signal bipolar polarization and strain (A and B), as well as the small signal e 0 r , tan(d), and d 33 as a function of bias field (C-D). Consistent with incipient piezoelectrics, BNT-25ST displays large polarization and Core-shell geometry Relevant so far exclusively for core-shell nanoparticles and their physical features, 88 thus not treated here Modification of synthesis route [105][106][107][108][109][110][111][112] Symmetry of core and shell 86,89,118 Modification of resistance, DC degradation, temperature-dependence of dielectric properties. 86,89,118 Sintering atmosphere 59 Coherency of interface: Semicoherent 71,75,80 or coherent 67,75,115 interfaces with chemically sharp or diffuse boundaries Increase in temperature stability of dielectric properties with coherency 56 Chemical modifications 56 Volumetric ratio of core-to-shell 67,73,81,119,120 Increase in overall relative permittivity with increasing core fraction.…”

“…The core–shell approach is an alternative route to achieve high and reliable electromechanical properties with a reduced hysteresis. Core–shell materials have been successfully implemented into dielectrics with exceptional, temperature stable properties . Although this approach holds much promise for piezoelectrics, it has been to date barely studied.…”

Microstructure effects on BaTiO3/BaTi0.8Zr0.2O3 composites properties

“…However, in order to meet the technological requirements that these devices must satisfy, i.e. high dielectric constant, low dielectric loss and temperature stability of properties, BaTiO3 must be modified [6], for example, by the development of layered ceramics. Using this approach, Ota et al [7] produced Ba1-xSrxTiO3-based capacitors with a temperature-independent electrical permittivity.…”