Silver Niobate Research Articles

Lead-Free Antiferroelectric Silver Niobate Tantalate with High Energy Storage Performance.

Antiferroelectric materials that display double ferroelectric hysteresis loops are receiving increasing attention for their superior energy storage density compared to their ferroelectric counterparts. Despite the good properties obtained in antiferroelectric La-doped Pb(Zr,Ti)O3 -based ceramics, lead-free alternatives are highly desired due to the environmental concerns, and AgNbO3 has been highlighted as a ferrielectric/antiferroelectric perovskite for energy storage applications. Enhanced energy storage performance, with recoverable energy density of 4.2 J cm-3 and high thermal stability of the energy storage density (with minimal variation of ≤±5%) over 20-120 °C, can be achieved in Ta-modified AgNbO3 ceramics. It is revealed that the incorporation of Ta to the Nb site can enhance the antiferroelectricity because of the reduced polarizability of B-site cations, which is confirmed by the polarization hysteresis, dielectric tunability, and selected-area electron diffraction measurements. Additionally, Ta addition in AgNbO3 leads to decreased grain size and increased bulk density, increasing the dielectric breakdown strength, up to 240 kV cm-1 versus 175 kV cm-1 for the pure counterpart, together with the enhanced antiferroelectricity, accounting for the high energy storage density.

Synthesis and crystal structure of pyrochlore-type silver niobate and tantalate

Synthesis and crystal structure of pyrochlore-type silver niobate and tantalate

Phase transitions in bismuth-modified silver niobate ceramics for high power energy storage

Ceramics of composition Ag1−3xBixNbO3 (0.005 ≤ x ≤ 0.040) were prepared by solid state methods and their structure and electrical behavior were characterized with a view to their potential use as high power energy storage materials.

Converting Ag nanowire into one-dimensional silver niobate and their enhanced photocatalytic activity

We synthesized one-dimensional silver niobate using Ag nanowires as the raw material and template. The final sample is the Ag2Nb4O11/AgNbO3 composite with a uniform distribution of elements, judging from the element analysis. In comparison with the pristine AgNbO3, the composite sample exhibits the enhanced photocatalytic activity for rhodamine B and 2,4-dichlorophene degradation under visible-light irradiation.

New AgNbO4−δ compound with high visible light photocatalytic activity

A new visible light responsive silver niobate photocatalyst AgNbO4−δ was synthesized by using a low-temperature chemical precipitation method. X-ray diffraction (XRD) results indicated that the AgNbO4−δ compound has a tetragonal scheelite (ABO4) type structure. It has also an optical absorption edge at about 596nm, corresponding to a bandgap of about 2.08eV. In addition, its microstructure and element composition were studied by using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS). Furthermore, its photocatalytic activities were evaluated in terms of degradation of Rhodamine B, showing that the as-prepared AgNbO4−δ compound has higher photocatalytic activity than P25.

High energy density in silver niobate ceramics

Solid-state dielectric energy storage is the most attractive and feasible way to store and release high power energy compared to chemical batteries and electrochemical super-capacitors.

Ferroelectric domain of epitaxial AgNbO3 thin film

We investigated ferroelectric properties of silver niobate (AgNbO3) thin film grown on Nb-doped SrTiO3 substrate by pulsed laser deposition. The AgNbO3 thin film exhibited room temperature ferroelectricity with a large remanent polarization of about 31μC/cm2 (2Pr~62μC/cm2) and fast switching behavior within 120ns. Triangular grains of AgNbO3 thin film were observed by atomic force microscopy (AFM). The piezoelectric force microscopy (PFM) study revealed that the AgNbO3 thin film had mosaic-like ferroelectric domain structure. In comparison with PbTiO3 thin films, domain size of the AgNbO3 thin films was smaller than that of PbTiO3 thin films. Based on Landau, Lifshitz, and Kittel (LLK) scaling law of the domain size versus film thickness curves, it is inferred that AgNbO3 thin films have slightly lower domain wall energy than that of PbTiO3 thin films.

Dielectric, ferroelectric and impedance spectroscopic study of Ta2O5, Sb2O5, and V2O5-doped AgNbO3 ceramic

In this work, silver niobate (AgNbO3) was doped with X2O5 (where, X = Ta, Sb, and V) and the series of samples were prepared by the solid state route. Phase analysis was carried out by the X-ray diffraction technique and the image of the surface morphology of each sample was taken by the Field emission scanning electron microscopy. Complex impedance spectroscopy was used to distinguish the different microstructure contribution in the conduction mechanism. Relaxation behaviour was observed in the imaginary part of impedance Z″(f) and electric modulus M″(f). The appearance of single semicircle in Cole–Cole of (Z′ vs. Z″) and (M′ vs. M″) confirmed a single relaxation process which was identified due to the intrinsic (grain) effect. The absence of any extrinsic interfacial conduction suggested that charge carriers at grain boundaries and sample surface are not activated properly. Therefore, it was presumed that no effective role by the metallic precipitated silver nano particles in electric properties within the chosen temperature range (25 °C–450 °C) containing major dielectric anomalies. The changes in the dielectric and ferroelectric behaviours were also discussed accordingly.

Ferroelectric domain switching kinetics of a lead-free AgNbO3 thin film on glass substrate

Lead-free silver niobate (AgNbO3) thin film was deposited on glass substrate by pulsed laser deposition. Ferroelectric properties of the AgNbO3 thin film were investigated. The AgNbO3 thin film capacitor exhibited good ferroelectricity with a remnant polarization of about 15.7μC/cm2 (2Pr ∼ 31.4μC/cm2) at room temperature and fast switching behavior within about 130ns. Triangular grains on the ANO thin film surface were observed by atomic force microscopy (AFM). By using piezoelectric force microscopy (PFM), we investigated ferroelectric domain switching and domain wall motion of the AgNbO3 thin film. From the domain wall speed as a function of applied electric field in the AgNbO3 thin film, activation energy of domain wall motion was derived. Compared to the PbTiO3 thin film reported previously, the AgNbO3 thin film showed faster switching behavior which could be attributed to its lower activation energy for domain wall motion.

Surface plasmon resonances behavior in visible light of non-metal perovskite oxides AgNbO3

We investigate the surface plasmon resonances (SPRs) behavior of silver niobate (AgNbO3) experimentally and theoretically. Result shows that the localized SPRs (LSPRs) of AgNbO3 combining with its interband transitions enlarge the absorption band across the whole ultraviolet-visible range. The LSPRs behavior in visible-light is mainly ascribed to the metal-like state of silver ion and self-assembled microstructures of AgNbO3 microcrystal. The ab initio density functional theory calculations are carried out to obtain the further insight of the SPRs behaviors. Theoretical study indicates that the Ag atoms are weakly bound in the perovskite structure, leading to a metal-like state, which was the key factor to SPRs behavior of AgNbO3.

Silver deficiency and excess effects on quality, dielectric properties and phase transitions of AgNbO3 ceramics

Silver niobate AgNbO3 is a promising basic compound for high permittivity microwave dielectrics and lead-free piezoelectrics. Stoichiometric and nonstoichiometric AgxNbO2.5+x/2 ceramics were obtained for x equal to 0.95, 0.98, 1.00, 1.02, and 1.05. Scanning electron microscopy and X-ray diffraction studies showed that the homogeneity of the perovskite phase and thus the ceramics quality improved with the increase of x. Dielectric and thermal measurements (DSC) were carried out in wide temperature range. They revealed that the phase transitions become less diffused and shift towards higher temperatures with the increase of silver concentration. These temperature shifts are more significant for the low temperature phase transitions, which are connected with appearance of the polar ferroelectric and antiferroelectric states, than for high temperature transitions related to oxygen octahedra tilts. Influence of silver concentration on interaction between electric dipoles and on stability of polar phases is discussed. A few percent silver excess improve significantly ceramic quality.

7Li NMR study of milling effects on instability of lithium-sites in lithium substituted silver niobate

Abstract Site occupation and structural change in Li substituted AgNbO 3 were probed by 7 Li NMR. Characteristic changes in the 7 Li NMR spectra depending on Li content were observed. Analysis of integrated intensity of the spectra revealed that 16% of substituted Li + ions occupy quasi-stable sites induced in crystal structure at 300 K in the 5 mol% Li substituted sample and would be in the state of motion, which are comparable to that of Li + ion in LiNbO 3 at high temperature. On the other hand, it was found that the Li + /Ag + sublattice in the 12.5 mol% Li substituted sample is easily made unstable by structural disturbance introduced in structure and the instability of the sublattice stimulates a local Li + ion motion via quasi-stable sites at room temperature. An appearance of the quasi-stable sites in local structure due to the Li substitution is closely related to instability of the Li/Ag sublattice and Li + ion dynamics in Li substituted AgNbO 3 .

Origin of the Ferrielectricty and Visible-Light Photocatalytic Activity of Silver Niobate AgNbO3

Silver niobate AgNbO3 is the important mother compound of lead-free ferroelectric AgNbO3–based materials and photocatalyts. The AgNbO3 has the ferrielectric structure with orthorhombic Pmc21 space group, but the origin of the ferrielectricity of AgNbO3 is unclear. Here, we report the results of electronic-structure calculations of the ferrielectric orthorhombic Pmc21 AgNbO3 in order to discuss the origin of the ferroelectricity and visible-light photocatalytic activity. We found the covalent Nb–O and Ag–O bonds in the ferrielectric AgNbO3. The covalent character is ascribed to the Nb 4d-O 2p and Ag 4d-O 2p hybridizations in AgNbO3. The Nb–O and Ag–O hybridization would be a key factor of the off-center displacements of Nb and Ag cations along the c axis, which induces the ferrielectricity in AgNbO3. The covalent bonds and the existence of Ag atom are responsible for the visible-light response of AgNbO3 photocatalyst.

Hydrothermal Syntheses and Structural Phase Transitions of AgNbO3

The phase‐pure AgNbO3 has been prepared through the hydrothermal reactions of NH4HF2, Ag2O, and Nb2O5. The room‐temperature powder X‐ray diffraction analysis reveals that it crystallizes in orthorhombic perovskite lattice with a space group of Pmc21 and cell parameters a = 15.6999(9), b = 5.5521(1), and c = 5.5830(1) Å. The temperatures, pH values, and times play crucial roles in obtaining phase‐pure silver niobate. The structural phase transitions were observed at 813 K from cubic to tetrahedral phase and to final orthorhombic phase at 718 K, confirmed by TGA‐DTA.

Effects of a site substitution of bivalent ions on Ag(Nb0.8Ta0.2)O3 ceramics

Bivalent ions equivalent substitution and equimolar substitution for Ag+ in silver niobate tantalate ceramic were studied, which will result in Ag0.98A0.01(Nb0.8Ta0.2)O3 and Ag0.98A0.02 (Nb0.8Ta0.2)O3 respectively, where A2+ = Mg2+, Ca2+, Sr2+, Ba2+, Cu2+, Pb2+. The samples were synthesized by traditional solid method and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The effects of a little Ag+ (in mol ratio 2 %) on the dielectric properties in Mg2+, Ca2+, Sr2+, Ba2+, Cu2+, Pb2+ substituted samples, and the influences of radius and ionic electronegativity on the dielectric properties were discussed. The results showed that the substitution of most bivalent ions except large Ba2+ ions for a little Ag+ (in mol ratio 2 %) showed no obvious change on the perovskite structure and microstructure of Ag(Nb0.8Ta0.2)O3 ceramics. Basically, the dielectric properties of equivalent substituted samples were better than that of equimolar equimolar substituted samples, Ca2+ equivalent substituted samples showed lower dielectric loss, and Cu2+ equivalent substituted samples showed higher dielectric constant.

Adaptive NbN/Ag coatings for high temperature tribological applications

Nanocomposite films that consist of niobium nitride with silver nanoinclusions were created using unbalanced magnetron sputtering to investigate their potential as adaptive, friction reducing coatings. The coatings were tribotested against a Si3N4 counterface in the 25 to 1000°C temperature range. The coatings displayed coefficients of friction in the 0.15 to 0.30 range at T>700°C. Post-wear testing structural and chemical characterization revealed that, in the low to mid-temperature range, silver migrated to the surface to reduce friction. At higher temperatures, oxygen, silver and the transition metal reacted to form lubricious binary metal oxide phases (silver niobate) in addition to pure silver. In situ Raman spectroscopy measurements were taken during heating and wear testing at 750°C to identify the evolution of phases in the coatings surface and in the wear track. The analysis of the in situ Raman spectroscopy data revealed the various stages of formation of these binary metal oxides. The coatings were subsequently doped with MoS2 to investigate the effect of the introduction of a low temperature lubricant. The addition of MoS2 did not appreciably reduce the room temperature coefficient of friction, likely due to the miscibility of this compound with the transition metal nitride. However, the coefficient of friction was significantly reduced at high temperatures because of the synergistic lubricious effect of silver niobates and molybdates.

Surface photoelectric and photodegradation activities of AgNbO 3 synthesized by solvothermal method

Silver niobate (AgNbO 3) with different morphologies is obtained by annealing the precursors prepared at different temperatures by solvothermal method at 800 °C. Scanning electron microscope images of the samples show the formation process of the morphologies. The weakest photovoltaic and the highest photocatalytic properties of the sample obtained from the precursors prepared at 190 °C are possibly caused by the synergetic effects between several kinds of particles, and between AgNbO 3 and Nb 2O 5. Both the temperature and the amount of Nb 2O 5 are crucial for the morphologies, the photoelectric and photocatalytic properties of the samples.

Phase transformations and properties of Ag1 − y NbO3 − y/2 (0 ≤ y ≤ 0.20) ceramics

We have studied the phase transformations, microstructure, and dielectric, piezoelectric, and thermophysical properties of Ag1 − yNbO3 − y/2 (0 ≤ y ≤ 0.20) ceramics. Within its homogeneity range (y ≤ 0.10), silver niobate undergoes a complex sequence of phase transformations, accompanied by anomalies in its physical properties. The observed dispersion effects are interpreted in terms of electrical conductivity above the Curie temperature and in terms of the motion of domain walls and interfaces below the Curie temperature.

Structure of Ferroelectric Silver Niobate AgNbO3

Crystal structure of ferroelectric silver niobate AgNbO3 was determined (Pmc21) by convergent beam electron, electron, neutron, and synchrotron diffraction techniques and first-principles calculations. The atomic displacements along the c axis in Pmc21 AgNbO3 are responsible for the spontaneous polarization, ferroelectricity, and the paraelectric−ferroelectric phase transition.

Ferroelectricity of Li-doped silver niobate(Ag, Li)NbO3

Phase evolution in (Ag1 − xLix)NbO3 (ALN) solid solution was investigated by the x-ray diffraction technique, dielectricand polarization measurements. It is shown that a small substitution of Ag withLi gives rise to an orthorhombic–rhombohedral structural transformation inABO3-perovskite silver niobate at room temperature. Structural refinementsindicate that both the A- and B-site displacements contribute to thespontaneous polarization of the ferroelectric phase with symmetryR3c. Increasing Li-concentration enhances the ferroelectric rhombohedral distortion, resultingin an increase of the para-ferroelectric phase transition temperature and the polarization ofthe solid solutions.