Phase structure, dielectric properties, and relaxor behavior of (K0.5Na0.5)NbO3–(Ba0.5Sr0.5)TiO3 lead-free solid solution for high temperature applications

Abstract

The (1−x)(K0.5Na0.5)NbO3–x(Ba0.5Sr0.5)TiO3 (KNN-BST) solid solution has been synthesized by conventional solid-state sintering in order to search for the new lead-free relaxor ferroelectrics for high temperature applications. The phase structure, dielectric properties, and relaxor behavior of the (1−x)KNN-xBST solid solution are systematically investigated. The phase structure of the (1−x)KNN-xBST solid solution gradually changes from pure perovskite phase with an orthorhombic symmetry to the tetragonal symmetry, then to the pseudocubic phase, and to the cubic phase with increasing addition of BST. The 0.90KNN-0.10BST solid solution shows a broad dielectric peak with permittivity maximum near 2500 and low dielectric loss (<4%) in the temperature range of 100–250 °C. The result indicates that this material may have great potential for a variety of high temperature applications. The diffuse phase transition and the temperature of the maximum dielectric permittivity shifting toward higher temperature with increasing frequency, which are two typical characteristics for relaxor ferroelectrics, are observed in the (1−x)KNN-xBST solid solution. The dielectric relaxor behavior obeys a modified Curie–Weiss law and a Vogel–Fulcher relationship. The relaxor nature is attributed to the appearance of polar nanoregions owing to the formation of randon fields including local electric fields and elastic fields. These results confirm that the KNN-based relaxor ferroelectrics can be regarded as an alternative direction for the development of high temperature lead-free relaxor ferroelectrics.

Tuning of dielectric, pyroelectric and ferroelectric properties of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ceramic by internal clamping

“…It is an interesting phenomenon and similar response has been recently reported by a number of researchers. 12,17,[77][78][79] Additionally, low dielectric loss is observed in the phase transition range. It indicates that this material can be used in wide range of high temperature applications such as multilayer ceramic capacitors in automobiles.…”

“…A similar phenomenon also occurs at the B site of ABO 3 perovskite structure, which also possess different valencies and ionic radii. 77 The presence of random fields, including the local electric elastic fields, hinders long-range dipole alignment, and gives rise to PNRs. 77 These PNRs are isolated in BNT-BT-ST and are embedded in the disordered matrix, which results in relaxor behavior.…”

“…The relaxation behavior in ferroelectrics can be explained by many model theories such as composition fluctuation theory, superpara electricity theory, merging of micropolar regions into macropolar regions, and random-field model. 77,[81][82][83] The common point of these models is based on the local distortion of the crystal structure, giving rise to polar nano-regions (PNRs). 81 In solid solution of BNT-BT-ST, Na results in the formation of the local electric fields owing to the local charge imbalance and local elastic fields due to local structure distortions.…”

“…However, relaxor ferroelectric materials exhibit diffuse phase transition of dielectric permittivity. Under this circumstance, modified Curie-Weiss law is used which can be expressed as: 77,80 …”

Relaxor nature in lead-free Sr5LaTi3Nb7O30 tetragonal tungsten bronze ceramics

“…Temperature dependences of e 0 follow the Curie-Weiss (CW) law above $330 K for all the applied frequencies from 1 Hz to 10 MHz with the extrapolated critical temperature T CW % 146 K and the Curie-Weiss constant C $ 1.22 Â 10 5 K. The dielectric constant deviates from the CW law below 330 K, which is called the deviation temperature T D , 28,29 and indicates the diffuse behavior. The diffuse behavior of dielectric constant from T m to T D can be described by a modified Curie Weiss law 30,31 …”