Antiferroelectric order and Ta-doped AgNbO3 with higher energy storage density

Abstract

Antiferroelectric phenomenological theory can well depict the behavior of the antiferroelectric system, but how to quantitatively define the antiferroelectric order parameter based on the experimental results is still an open question. In this work, the reduced antiferroelectric order parameter is proposed based on the direct atomic-scale observation, which can be regarded as an extension of the traditional antiferroelectric order parameter. In addition, the enhancement of energy storage density of Ta-doped silver niobate is discussed using this reduced antiferroelectric order parameter as a tool. It is found that the deeper reason for the increase of energy storage density can be attributed to the decrease of the permittivity χ0 of the corresponding paraelectric phase, and novel antiferroelectric materials with high energy storage density may be realized on the base of it.

Local Structure Heterogeneity in Sm-Doped AgNbO3 for Improved Energy-Storage Performance

“…In AgNbO 3 , the polarity switching process is accomplished by Nb 5+ ions shifting within the equatorial plane ( ab plane) of NbO 6 octahedra (it should be noted that the shifting of Ag ions may also contribute to the polarization but is more complex) . Obviously, the polarization induced by this displacement is proportional to the effective charge and the displacement of the individual ion . As the ion displacement is constrained by rare-earth element doping, the contribution of the displacement to the total polarization will be limited, leading to decreased polarization of the ferroelectric phase.…”

“…Theoretically, E A and E F are larger than E 0 ; thus, an increased E 0 leads to increased E A and E F . A reasonable approximation of the critical electric field can be written as where η 0 is the antiferroelectric order parameter under zero electric field and χ 0 is the dielectric susceptibility (χ = ε r – 1, ε r is the relative dielectric permittivity as given in Figure a). It is clear that E 0 is inversely proportional to χ 0 3/2 , therefore, the critical electric field E 0 can be increased by decreasing the dielectric constant of the paraelectric phase or by increasing the antiferroelectric order parameter.…”

“…33 Obviously, the polarization induced by this displacement is proportional to the effective charge and the displacement of the individual ion. 34 As the ion displacement is constrained by rare-earth element doping, the contribution of the displacement to the total polarization will be limited, leading to decreased polarization of the ferroelectric phase.…”

Impact of Li Doping on the Structure and Phase Stability in AgNbO3

“…The niobate perovskites NaNbO 3 and AgNbO 3 have polar structures at room temperature and have been identified as promising lead-free replacements for the piezoelectric material PbZr 1– x Ti x O 3 (PZT) . Ceramics based on AgNbO 3 also show great potential as lead-free candidates for dielectric energy-storage applications. − The niobate perovskites are structurally complex as exemplified by NaNbO 3 , which shows a baffling array of temperature-dependent structural phase transitions. − High-resolution neutron diffraction studies have revealed the structural sequence in NaNbO 3 upon heating to be R 3 c → Pbcm → Pmmn → Pmmn → Cmcm → P 4/ mbm → Pm 3̅ m . , This sequence of phases is often described using the notation developed by Megaw as N → P → R → S → T 1 → T 2 → U . There is evidence that at room temperature a second orthorhombic phase in space group P 2 1 ma can coexist with the Pbcm (an alternate setting of Pcam ) phase of NaNbO 3 .…”

Observation of Ferroelastic and Ferroelectric Domains in AgNbO3 Single Crystal

“…[3] There are many different strategies to improve the energy storage performance of ferroic materials. [4][5][6] A comprehensive studies trying to modify or reshape the hysteresis loop for larger storage capacity have been demonstrated through A-site doping, [7][8][9][10][11][12] B-site doping [13,14] and simultaneously doping both sites. [15] However, there exists nontrivial and critical debates about the crystalline structure of ANO at room temperature.…”