Improved electrical properties for Mn-doped lead-free piezoelectric potassium sodium niobate ceramics

Abstract

The un-doped and doped lead-free piezoelectric potassium sodium niobate (K0.5Na0.5NbO3, KNN) ceramics with different amounts of Mn were prepared. The decreased dielectric losses and the improved electrical properties were observed in the Mn-doped KNN ceramics. However, the variation of electrical properties with the Mn contents was not continuously. The 0.5 mol.% Mn-doped KNN ceramic shows the highest dielectric loss and the worst electrical properties. The KNN ceramics doped with less than and more than 0.5 mol.% Mn all show improved electrical properties. The change of lattice position of Mn ions in KNN ceramics was the main reason. When the Mn content is less than 0.5 mol.%, the Mn ions occupied the cation vacancies in A-site. When the Mn content is higher than 0.5 mol.%, the Mn ions entered B-site of KNN perovskite structure and formed the defect complexes (MnNb″−VO⋅⋅) and (MnNb′−VO⋅⋅−MnNb′). They both led to a lower defect concentration. However, When the Mn content is up to 1.5 mol.%, the electrical properties of KNN ceramic became degraded because of the accumulation of Mn oxides at grain boundaries.

Temperature stability and electrical properties of MnO‐doped KNN‐based ceramics sintered in reducing atmosphere

“…The ferroelectric hysteresis loops of samples sintered in reducing atmosphere at x = 0.2‐0.4 are no significant change due to the priority occupation of Mn 2+ ions in cation vacancies. This phenomenon is consistent with that reported in the literature . The ferroelectric hysteresis loops area of samples become small at x = 0.6 and then turns to large at x = 0.8.…”

“…The peak located at the lower binding energy (158.60 eV) is attributed to Bi ions with low valence state, whereas the peaks located at higher binding energy (159.00 eV) is, respectively, attributed to the Bi 3+ ions. The Bi 4f 7/2 peak (159.00 eV) of Mn0 ceramic is slightly higher than that (158.90 eV) of Mn0‐air ceramics, which is similar to the behavior of Nb 3d 5/2 peak, because of the higher oxygen vacancy concentration . The binding energy of the used BiNbO4 catalysts show a 0.2 eV lower shift, corresponding to a reduction in the Bi in the catalyst .…”

“…The undoped KNN‐0.045BNZ ceramics should exist large distortion of O‐Nb‐O angles due to the alkali metal volatilization. In a literature, Mn ions preferentially enter cation vacancies, which can decrease the concentration of cation vacancies and make an alleviation of the large distortion of O‐Nb‐O angles . Thus, FWHM of MnO‐doped KNN‐0.045BNZ ceramics decreases at x = 0.2‐0.4.…”

“…The binding energy peak (206.50 eV) of Nb3d 5/2 for Mn0‐air ceramics shows lower than that (206.60 eV) of Mn0 ceramics. The cause of this phenomenon may be that the reducing atmosphere induces the formation of more oxygen vacancies in the ceramics, which increases the electron cloud density around the ion . The binding energy peak of 3d 5/2 for the samples sintered in reducing atmosphere remain unchanged at x = 0‐0.4, and then increases from 206.60 eV to 206.80 eV at x = 0.5‐0.8.…”

“…However, the cell volume of ceramics increases at x = 0.5‐0.8. Wang have reported that Mn ions prefer to occupy the cation vacancies in A‐site at 0%‐0.5% MnO content, which leads to unchanged cell volume. It is believed that the stable cell volume of samples sintered in reducing atmosphere is not expected from the substitution of K + (1.64 Å:12CN), Na + (1.39 Å:12CN), and Bi 3+ (1.39 Å:12CN) with Mn 2+ (1.27 Å:12CN) in the A‐site of the perovskite lattice .…”