The NbO₆ octahedral distortion and phase structural transition of Eu³⁺‐doped K_0.5Na_0.5NbO₃–xLiNbO₃ ferroelectric ceramics

Abstract

A small quantity of Eu 3+ ions were doped in the lead-free ferroelectric K 0.5 Na 0.5 NbO 3 -xLiNbO 3 (KNN-xLN, 0 ≤ x ≤ 0.08) ceramics to investigate the NbO 6 octahedral distortion induced by the increasing LN content. In addition, the phase structure, ferroelectric, and photoluminescence properties of K 0.5 Na 0. ions demonstrated that the prepared ceramics undergo a polymorphic phase transition (PPT, from orthorhombic to tetragonal phase transformation) with the rising LN content, and the PPT region locates at 0.05 ≤ x ≤ 0.06. The ferroelectric properties, Raman intensity ratios and photoluminescence intensity ratios show similar variations with the increasing LN content, all with a maximum value achieved at the PPT region. We believe that the close relationship among the ferroelectric properties, Raman intensity ratios, and photoluminescence intensity ratios is caused by the NbO 6 octahedral distortion. The photoluminescence of Eu 3+ ion was discussed basing on the crystal-symmetry principle and Judd-Ofelt theory. K E Y W O R D Selectrical properties, lead-free ceramics, luminescence, perovskites, phase transformations | INTRODUCTIONFerroelectric ceramics have attracted considerable attention due to their unique direct piezoelectric and converse piezoelectric properties, which could realize the interconversion between mechanical energy and electrical energy. 1-3 To achieve outstanding piezoelectric property, the basic approach is inducing a multiphase coexistence around room temperature through composition modification, and a large amount of works have been performed to investigate the morphotropic phase boundary (MPB) effect to enhance the piezoelectricity in lead-based ferroelectric ceramics.

Composite microstructures and piezoelectric properties in tantalum substituted lead-free K0.5Na0.5Nb1-xTaxO3 ceramics

“…For the end members x = 0 and x = 1, Raman spectra are consistent with the literature [46][47][48][49][50][51][52]. For x = 1, K0.5Na0.5TaO3 (KNT) crystallizes in a cubic structure with…”

“…However, the spectrum presents some peaks that might be attributed to second order Raman modes or even infrared modes, activated by some structural disorder [53][54]. For x = 0, the observed Raman spectrum is similar to that reported by several authors [46] for KNN and related compositions, and corresponds to the orthorhombic structure with Amm2 space group [46][47][48][49][50][51][52][55][56][57][58].. This spectrum can be described by means of internal vibrations of the octahedral NbO6 (Oh symmetry).…”

“…For KNN and related compositions, wavenumber of A1g (ν1) and Eg (ν2) modes in the region 500 -700 cm -1 were largely used to identify phase transitions [47][48][49]51,52,59]. Hence, both band modes were fitted to the sum of two Gaussian-Lorentzian curves and wavenumbers versus tantalum content is plotted in figs.…”

Quantitative analyses of electric field–induced phase transition in (Na, K)0.5Bi0.5TiO3:Eu ceramics by photoluminescence

“…Many ferroelectric ceramics doped with RE ions show efficient PL properties while maintaining their excellent electrical properties, making them multifunctional materials . It is generally believed that the optimal properties of ferroelectric ceramics can be achieved under condition of multiphase coexistence, such as morphotropic phase boundary (MPB) . In ferroelectric materials with compositions near MPB, the free energy difference between phases is small, which means that phase transition can be easily induced by external conditions such as stress and electric field .…”

Efficient red‐emitting phosphor of Eu3+‐activated (Na0.5Gd1.5)(TiSb)O7 derived via cation‐substitutions in Gd‐Pyrochlore

“…Second, microstructures of Eu 3+ ions can greatly influence the emission transitions of 5 D 0 – 7 F 2 (electric dipole) and 5 D 0 – 7 F 1 (magnetic dipole) . Eu 3+ ‐doped Gd 2 Ti 2 O 7 exhibits a typical yellow‐red luminescence color because of its cubic‐type host with the center of symmetry ( D 3d ) of Gd 3+ ions .…”