Abstract
A number of relaxor ferroelectric ceramics have been demonstrated to possess a near stable value of relative permittivity over very wide temperature ranges. This cannot be explained by conventional theories of relaxors. One such system is based on the perovskite solid solution series: (1-x) (Ba0.8Ca0.2)TiO3-xBi(Mg0.5Ti0.5)O3, giving stable relative permittivity from 150 to 500 °C. We show by scanning transmission electron microscopy and electron energy loss spectroscopic elemental mapping that nanoscale compositional segregation occurs in the temperature stable relaxor composition (x = 0.55), with Ba/Ti clusters some 2–4 nm in extent, separated by Bi-rich regions of comparable size. This nanomosaic structure is consistent with phase separation into a ferroelectrically active BaTiO3 – type phase (Ba/Ti rich) and a weakly polar Bi/(Mg) rich perovskite solid solution. The possibility that nanophase segregation is the cause of weak dipole coupling and suppression of the dielectric relaxation peak is considered.
Highlights
There is a growing requirement to develop new capacitor materials that can operate reliably at temperatures >200 C for use in electronic systems in harsh environments, for example engine control and management systems in the aerospace and automotive sectors, and for power electronics in the renewables sector
This paper reports the results of scanning transmission electron microscopy (STEM) analysis using both energy dispersive and electron energy loss spectrometries to probe the chemical composition of (1-x) (Ba0.8Ca0.2)TiO3-xBi(Mg0.5Ti0.5)O3, at a variety of length scales for both a composition exhibiting normal relaxor characteristics (x 1⁄4 0.1, Fig. 1a) and a temperature-stable composition with a severely suppressed dielectric peak (x 1⁄4 0.55, Fig. 1b)
No evidence of any weak reflections due to secondary phases was present in XRD patterns, indicating secondary microscale phases observed by STEM were present in only very minor quantities throughout the bulk ceramic [4,6]
Summary
There is a growing requirement to develop new capacitor materials that can operate reliably at temperatures >200 C for use in electronic systems in harsh environments, for example engine control and management systems in the aerospace and automotive sectors, and for power electronics in the renewables sector. Microscale chemical segregation induced by chemical doping creates a core shell grain structure which smears out the Curie peak. This approach has provided the basis for the present generation of high-temperature commercial Class II capacitors that exhibit stable capacitance C25C ±15% from a lower operating temperature of À55 C to an upper limit of 125 C in materials designated X7R by the Electronics Industries Alliance. Examples include the following solid solutions with substitution on A and B sites of the BaTiO3 perovskite lattice; BaTiO3-BiScO3, BaTiO3Bi(Mg0.5Ti0.5)O3, BaTiO3-Bi(Zn0.5Ti0.5)O3, and (Ba 0.8Ca0.2)TiO3Bi(Mg0.5Ti0.5)O3 [1e5] These systems can show a progression of dielectric properties from ferroelectric to diffuse ferroelectric through to a normal relaxor ferroelectric with broad frequencydependent dielectric peak (at Tm) at low to moderate levels of substitution
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
