Lead-free high-temperature dielectrics with wide operational range

Abstract

The dielectric, electrical and structural properties of (1–x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–xK0.5Na0.5NbO3 (BNT–BT–xKNN) with x=0.09, 0.12, 0.15, and 0.18 were investigated as potential candidates for high-temperature capacitors with a working temperature far beyond 200 °C. Temperature dependent dielectric permittivity (ε) showed two local broad maxima that at the optimal composition of KNN (x=0.18) are combined to form a plateau. This then results in a highly temperature-insensitive permittivity up to ∼300 °C at the expense of a small reduction in absolute permittivity values. High-temperature in situ x-ray diffraction study showed pseudocubic symmetry without obvious structural changes, which implies that the dielectric anomalies observed could only be a consequence of a slight change in space group. BNT–BT–0.18KNN showed a permittivity of ∼2150 at the frequency of 1 kHz at 150 °C with a normalized permittivity ε/ε150 °C varying no more than ±10% from 43 to 319 °C. With very good electrical properties persisting up to 300 °C, i.e., a resistivity on the order of magnitude of 108 Ω m and the RC constant of about 1 s, the examined BNT–BT–xKNN compositions present a good starting point for the development of high-temperature capacitor materials.

Incipient piezoelectrics and electrostriction behavior in Sn-doped Bi1/2(Na0.82K0.18)1/2TiO3 lead-free ceramics

“…There are two distinct anomalies evident in e r for all compositions: a shoulder at $150 C with a strong frequency dispersion and frequency-insensitive peaks at $300 C. The magnitude of overall dielectric signal is seen to decrease with increasing Sn content, while the temperature range for each anomaly remains practically invariant. Consistent observation has been reported in BT-BY, 24 BNT-BT, 27 and BNT-BKT 28 systems with additional chemical modifiers being introduced. On the other hand, an additional dielectric anomaly appears when the materials are electrically poled.…”

Low variation in relative permittivity over the temperature range 25–450°C for ceramics in the system (1−x)[Ba0.8Ca0.2TiO3]–x[Bi(Zn0.5Ti0.5)O3]

“…5 Bi 0.5 TiO 3 [1]; Na 0. 5 Bi 0.5 TiO 3 -0.06BaTiO 3 -K 0.5 Na 0.5 NbO 3 [2]; Na 0. 5 Bi 0.5 TiO 3 -K 0.…”

“…Ceramics with stable dielectric properties at temperatures >200 °C offer opportunities for developing high-temperature capacitors for applications in electronic control systems for hybrid or electrically powered vehicles [1,2]. The dielectric material must have high and uniform dielectric permittivity, r , coupled to low dielectric loss over a wide operating temperature range.…”

High temperature dielectric ceramics: a review of temperature-stable high-permittivity perovskites

“…Dittmer et al, Technical University Darmstadt, studied the ternary system, (1-x)(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-xK0.5Na0.5NbO3, [NBT-BT-KNN] for compositions x ≤ 0.18 KNN [49]. In a similar manner to NBT-based materials reported by Li et al, for the Na0.5Bi0.5TiO3-NaNbO3 system, and by Bridger et al, for complex compositions based on NBT [45,46].…”