Structure transition and electric properties in lead-free (Na0.5K0.5)1-xAgxNb1-xTaxO3 ceramics with the polymorphic phase boundary region

• Published in: Journal of solid state chemistry Vol. 316
• Main Authors: Wang, L.G., Huang, X.X., Zhu, C.M., Yu, G.B., Su, X.F., Huang, R.T., Qin, H.X., Kong, W.J.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.12.2022
• Subjects: (Na0.5K0.5)1-xAgxNb1-xTaxO3; Dielectricity; Ferroelectric ceramics; Piezoelectricity; Polymorphic phase boundaries; (Na0.5K0.5)1-xAgxNb1-xTaxO3; Piezoelectricity; Ferroelectric ceramics; Polymorphic phase boundaries; Dielectricity
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2022.123552

The (Na0.5K0.5)1-xAgxNb1-xTaxO3 series have been well synthesized with structure distortion tendency from orthorhombic to orthorhombic/tetragonal coexistence phase as component ratio varies from x ​= ​0 to 0.15, which is confirmed through X-ray diffraction patterns and Raman spectra. Moreover, polymorphic phase boundary region is affirmed of the sample with x ​= ​0.075, accompanied by the maximum value for piezoelectric coefficient. The reversible transition between relaxor and ferroelectric phase is measured with increasing Ag+ and Ta5+ ions. For the sample of x ​= ​0.075, the evolution of polarization properties from relaxor to ferroelectric phase with increasing temperature is interpreted by the crystal transition during the polarization reversal process. Moreover, the critical temperature of ∼200 ​°C at x ​= ​0.075 is consistent with the dielectric and Raman properties with increasing temperature. The obtained results suggest (Na0.5K0.5)1-xAgxNb1-xTaxO3 ceramics might be promising for high temperature electric applications. Raman analysis is performed for all the NKAxNTx samples with frequency varying from 100 to 1000 ​cm−1, as presented in Fig. 4(a). In order to specify the vibration frequency, the deconvolution of spectrum for NKN is presented in the bottom of Fig. 4(a). Fig. 4(b–d) display the fitting result of the samples with x ​= ​0, 0.075 and 0.15 during 480–720 ​cm−1. The left inset of Fig. 4(a) is the wavenumber shift as function of x at ∼258 and ∼615 ​cm−1. The right inset of Fig. 4(a) is the intensity ratio of ∼550 ​cm−1 compared with that at ∼615 ​cm−1, which verifies the softening of mode at ∼550 ​cm−1. [Display omitted] •(Na0.5K0.5)1-xAgxNb1-xTaxO3 ceramics (x ​= ​0–0.15) are synthesized by solid state reaction.•Polymorphic phase boundary can be confirmed during crystal transition process.•Electric properties show the transition behavior between ferroelectric order and relaxor state.