Novel High‐Temperature Antiferroelectric‐Based Dielectric NaNbO₃–NaTaO₃ Solid Solutions Processed in Low Oxygen Partial Pressures

Abstract

The (1−x)NaNbO 3 -(x)NaTaO 3 solid solution was investigated for x ≤ 0.4 in terms of new high-temperature and high-permittivity dielectric system that is suitable for base metal inner electrode capacitor applications. The addition of Ta significantly enhanced the resistivity of the dielectric, resulting in superior resistivity than the dielectrics-formulated BaTiO 3 systems that dominate the multilayer ceramic capacitor dielectric devices. The voltage dependence of the permittivity was also superior to BaTiO 3 -based materials, providing higher capacitance at higher temperatures. A transmission electron microscopy study illustrated that the grains had so-called core-shell structure. According to the electron diffraction analysis, the core region had an inhomogeneous structure between antiferroelectric and ferroelectric phases, and shell region had an incommensurate ferroelectric-like structure. The core and shell region had Nb-and Ta-rich composition, respectively, and their interface was compositionally sharp, implying that shell region was formed via a liquid phase during the sintering process with an incongruent Ta dissolution reprecipitation. We anticipate that these or similar materials based on the alkali-niobate perovskites can be further enhanced to provide capacitor solutions from 150°C to 250°C, which is an important range for a number of new AC-DC invertor and engine control units.

Strategy for stabilization of the antiferroelectric phase (Pbma) over the metastable ferroelectric phase (P21ma) to establish double loop hysteresis in lead-free (1−x)NaNbO3-xSrZrO3 solid solution

“…1,2 As motivated by the need to design ecofriendly piezoelectric ceramics during the past decade, [3][4][5][6][7][8][9] the exploration of lead-free AFE dielectrics over the lead-containing ones, such as PbZrO 3 -based systems, has also evoked considerable interest. 2,[10][11][12][13][14] The NaNbO 3 -based ceramics have been extensively studied due to the intrinsic AFE nature of NaNbO 3 , which is commonly referred to as P phase (with space group Pbma) at ambient conditions. [15][16][17][18] However, the AFE characteristic double P-E hysteresis loops are rarely observed in these systems due to a metastable ferroelectric (FE) Q phase (with space group P2 1 ma), 18 which displays a comparable free-energy profile with the AFE P phase and can be easily induced, and hence prevent back-switching to the AFE state.…”

Enhancement of Piezoelectric Performance of Lead‐Free NKN‐Based Ceramics via a High‐Performance Flux—NaF–Nb2O5

“…However, pure NKN ceramics are difficult to be fully densified via conventional routes due to the high volatility of alkaline elements at high sintering temperatures in air atmospheres. Therefore, different methods have been utilized to solve this problem, such as pressure‐assisted sintering (PAS), spark plasma sintering (SPS), vacuum sintering and low partial pressures of oxygen (low p O 2 ) sintering . Compared with the traditional sintering process, PAS and SPS methods work at laboratory scale, but there are concerns about the scaling up and industrial feasibility of these sintering technologies for the piezoelectric industry.…”

“…Therefore, different methods have been utilized to solve this problem, such as pressure-assisted sintering (PAS), spark plasma sintering (SPS), vacuum sintering and low partial pressures of oxygen (low pO 2 ) sintering. [17][18][19][20][21] Compared with the traditional sintering process, PAS and SPS methods work at laboratory scale, but there are concerns about the scaling up and industrial feasibility of these sintering technologies for the piezoelectric industry. Recent studies on low pO 2 -cofired NKN with nickel inner electrodes demonstrate an effective approach to narrow the performance gap between lead-based and lead-free piezoelectric systems.…”

Antiferroelectricity induced by electric field in NaNbO3-based lead-free ceramics

“…[13][14][15][16][17] Its solid solutions are of technological importance due to applications in lead-free piezoelectric devices [18][19][20] and high-temperature capacitors. 21 Although NaNbO 3 has been investigated for more than six decades, researchers are still debating whether it is antiferroelectric or ferroelectric at room temperature. 22 It seems that the confusion roots at the appearance of the polarization vs. electric field hysteresis loops.…”