Structural, Dielectric, Pyroelectric and Ferroelectric Properties of Glass Nano Composite: Lithium Borate-Strontium Bismuth Vanadium Niobate

Transparent glasses in the system (100−x) $(Li_2O-2B_2O_3)-x (SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5)$ $(10 \le x \le 60$, in molar ratio) were fabricated via the melt quenching technique. The as-quenched samples were X-ray amorphous. Differential thermal analysis (DTA) confirmed the glassy nature of the as-quenched samples. Strontium bismuth vanadium niobate nanorods were grown by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. The formation of nanorod layered perovskite $SrBi_2(Nb_{0.7}V_{0.3})_2O_{9-\delta}$ (SBVN) phase via an intermediate fluorite phase was confirmed by both X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The dielectric constants of both the as-quenched and heat-treated samples (783 K/6 h) increased while the dielectric loss (D) decreased with increasing x (SBVN content). Interestingly, the dielectric constant of the glass nanocrystal composite (heat-treated at 783 K/6 h) exhibited an anomaly in the vicinity of the crystallization temperature of the host glass $(Li_2B_4O_7)$ reaching a value as high as $\approx 10^6$ at 800 K. These glass nanocrystal composites were pyroelectric and ferroelectric at 300 K

The Microstructural, Dielectric, Pyroelectric and Ferroelectric Properties of SrBi2(Nb1−xVx)2O9(0≤x≤0.3)SrBi_{2}(Nb_{1-x}V_{x})_{2}O_{9}(0 \leq x \leq 0.3) Ceramics

Layered $SrBi_{2}(Nb_{1-x}V_{x})_{2}O_{9}$ (SBVN) ceramics with x ranging from 0 to 0.3 (30 mol%) were fabricated via the conventional sintering technique.A remarkable transformation in the microstructure of SBN ceramic was encountered as the $V_{2}O_{5}$ content increased from 3-30 mol%. The average grain size of the SBN ceramic containing $V_{2}O_{5}$ was found to increase with increase in $V_{2}O_{5}$ content. The dielectric constant $(\epsilon_{r})$ as well as the dielectric loss (D) increased with increase in grain size(6 \mu m-17 \mu m). The ferroelectric to paraelectric transition temperature $(T_{c})$ shifted to higher temperature with increasing grain size. The pyroelectric coefficient was positive at 300 K and increased with increasing grain size. Interestingly, the $SrBi_{2}(Nb_{1-x}V_{x})_{2}O_{9}$(x = 0.3) ceramics with a grain size of 17 \mu m exhibited higher remnant polarization $(P_{r})$ and lower coercive field $(E_{c})$ than those with grains of 7 \mu m. The Curie-Weiss constant that was obtained for these ceramics was in line with that of displacive type ferroelectrics

Frequency-dependent dielectric characteristics of ferroelectric SrBi2Nb2O9SrBi_2Nb_2O_9 ceramics

The dielectric properties of ferroelectric $SrBi_2Nb_2O_9$ (SBN) ceramics have been studied in the frequency range of 100 Hz to 1 MHz at various temperatures (300–823 K). A strong low frequency dielectric dispersion (LFDD) is encountered in these ceramics in the 573–823 K temperature range. Electrical conductivity data indicate that the conductivity in SBN is essentially due to oxygen vacancies and the activation energy for the conduction in the high temperature region is found to be 0.90 eV. The dielectric constants measured as a function of frequency (100 Hz–1 MHz) in the 300–823 K temperature range have been found to fit to the Jonscher’s dielectric dispersion relations: $\varepsilon_r' = \varepsilon_\infty+ sin(n(T)\pi/2)\omega^{n(T) - 1}a(T)/\varepsilon_o$ and $\varepsilon_r" = \sigma/\varepsilon_o\omega+ cos(n(T)\pi/2)\omega^{n(T)-1}a(T)/\varepsilon_o.$ The high frequency (1 MHz) dielectric constant $(\varepsilon_\infty)$ shows a peak at $T_c$ (723 K).The coefficient A(T) (=a(T)S/L) and the exponent n(T) of the Jonscher’s expression are determined. The exponent n(T) is found to be minimum at the Curie temperature, $T_c.$ The parameter A(T), which indicates the strength of the polarizability, shows a prominent peak in the vicinity of the Curie temperature

The influence of microscopic parameters on the ionic conductivity of SrBi2(Nb1−xVx)2O9−δ(0≤x≤0.3)SrBi_{2}(Nb_{1-x}V_{x})_{2}O_{9-\delta}(0 \leq x \leq 0.3) ceramics

Layered $SrBi_{2}(Nb_{1-x}V_{x})_{2}O_{9-\delta}$(SBVN) ceramics with x lying in the range 0-0.3 (30 mol%) were fabricated by the conventional sintering technique. The microstructural studies confirmed the truncating effect of $V_{2}O_{5}$ on the abnormal platy growth of SBN grains. The electrical conductivity studies were centred in the 573-823 K as the Curie temperature ties in this range. The concentration of mobile charge carriers (n), the diffusion constant $(D_{O})$ and the mean free path (a) were calculated by using Rice and Roth formalism. The conductivity parameters such as ion-hopping rate $(\omega_{p})$ and the charge carrier concentration (K') term have been calculated using Almond and West formalism. The aforementioned microscopic parameters were found to be $V_{2}O_{5}$ content dependent on $SrBi_{2}(Nb_{1-x}V_{x})_{2}O_{9-\delta}$ ceramics

Frequency Dependent Dielectric Characteristics of Undoped and Vanadium-Doped SrBi2Nb2O9SrBi_{2}Nb_{2}O_{9} Ferroelectric Ceramics: A Comparative Study

The dielectric properties of undoped and vanadium (10 mol%) doped $SrBi_{2}Nb_{2}O_{9}$ ferroelectric ceramics were studied in the 100 Hz to 1 MHz frequency range at various temperatures (300-823 K). The dielectric constants of vanadium doped ceramics were higher than those of undoped ceramics. A strong low frequency dielectric dispersion (LFDD) was encountered in these ceramics in the 573-823 K temperature range. The dispersion was stronger at low frequencies and higher temperatures for vanadium - doped ceramics. The dielectric constants measured in the wide frequency and temperature ranges for both the samples were found to fit well to the Jonscher's dielectric dispersion relations: \epsilon_{r}^{'} = \epsilon_{\infinity} + sin (n(T)\pi /2) \omega^{n(T)-1} a(T)/\epsilon_{o} and \epsilon_{r}^{''} = \sigma/\epsilon_{o} \omega + cos (n (T) \pi /2) \omega^{(n(T)-1} a(T)/\epsilon_{o}. The lattice dielectric constant (\epsilon_{\infinity}) shows a peak at $T_{c}$. The coefficient A(T)(= a(T)S/L) and the exponent n (T) of the Jonscher's expression were determined. The exponent n (T) was found to be minimum at the Curie temperature, $T_{c}$ . The value of n for the vanadium-doped samples was less than that of the undoped one. The parameter A(T), which indicates the polarizing power, showed a prominent peak in the vicinity of the Curie temperature for both the samples. However, the value of A for the vanadium-doped samples was higher than that of undoped SBN ceramics

Electrical properties of SrBi_2(Nb_0_._7V_0_._3)_2O_9_-_{\delta} in the SrO–Bi2O3–0.7Nb2O5–0.3V2O5–Li2B4O7SrO–Bi_2O_3–0.7Nb_2O_5–0.3V_2O_5–Li_2B_4O_7 glass system

Glasses in the system $(100-x)Li_2B_4O_7–x(SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5)$ (where x = 10, 30 and 50, in molar ratio) were fabricated via melt quenching technique. The compositional dependence of the glass transition $(T_g)$ and crystallization (T_c_r) temperatures was determined by differential thermal analysis. The as-quenched glasses on heat-treatment at 783 K for 6 h yielded monophasic crystalline strontium bismuth niobate doped with vanadium (SrBi_2(Nb_0_._7V_0_._3)_2O_9-_{\delta} (SBVN)) in lithium borate (Li2B4O7 (LBO)) glass matrix. The formation of nanocrystalline layered perovskite SBVN phase was preceded by the fluorite phase as established by both the X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The dielectric constants for both the as-quenched glass and glass–nanocrystal composite increased with increasing temperature in the 300–873 K range, exhibiting a maximum in the vicinity of the crystallization temperature of the host glass matrix. The electrical behavior of the glasses and glass–nanocrystal composites was characterized using impedance spectroscopy

Structural and optical properties of (100−x)(Li2B4O7)−x(SrO−Bi2O3−0.7Nb2O5−0.3V2O5)(100-x)(Li_2B_4O_7)-x(SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5) glasses and glass nanocrystal composites

Glasses of various compositions in the system (100-x)({Li_2B_4O_7})-x(SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5}) $(10\leq x \leq 60$, in molar ratio) were prepared by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Glass composites comprising strontium bismuth niobate doped with vanadium (SrBi_2(Nb_{0.7}V_{0.3})_2O{_9{_-_\delta} (SBVN)) nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. High resolution transmission electron microscopy (HRTEM) of the glass nanocrystal composites (heat-treated at 783 K/6 h) confirm the presence of rod shaped crystallites of SBVN embedded in ${Li_2B_4O_7}$ glass matrix. The optical transmission spectra of these glasses and glass nanocrystal composites of various compositions were recorded in the wavelength range 190–900 nm. Various optical parameters such as optical band gap $(E_{opt})$, Urbach energy $(\Delta E)$, refractive index (n), optical dielectric constant $(\epsilon ^{\prime}_\infty)$ and ratio of carrier concentration to the effective mass $(N/m ^\ast)$ were determined. The effects of composition of the glasses and glass nanocrystal composites on these parameters were studied

Influence of Sm2O3 doping on formation and structure of SrBi2Nb2O9 nanocrystals in lithium borate glasses

New glasses of 16.66SrO–16.66[(1 − x)Bi2O3–xSm2O3]–16.66Nb2O5–50Li2B4O7 (0 ≤ x ≤ 0.5, in molar ratio), i.e., the pseudo-binary Sm2O3-doped SrBi2Nb2O9–Li2B4O7 glass system, giving the crystallization of Sm3+-doped SrBi2Nb2O9 nanocrystals are developed. It is found that the thermal stability of the glasses against the crystallization and the optical band gap energy increases with increasing Sm2O3 content. The formation of fluorite-type Sm3+-doped SrBi2Nb2O9 nanocrystals (diameters: 13–37 nm) with a cubic structure is confirmed in the crystallized (530 °C, 3 h) samples from X-ray powder diffraction analyses, Raman scattering spectrum measurements, and transmission electron microscope observations. The effect of Sm3+-doping on the microstructure, Raman scattering peak positions, and dielectric properties of composites comprising of fluorite-type SrBi2Nb2O9 nanocrystals and the Li2B4O7 glassy phase is clarified. It is found that fluorite-type SrBi2Nb2O9 nanocrystals transform to stable perovskite-type SrBi2Nb2O9 crystals with an orthorhombic structure by heat treatments at around 630 °C

Optical diffraction of second harmonic generation in SrBi2(Nb0.7V0.3)2O9 in the SrO–Bi2O3–0.7Nb2O5–0.3V2O5–Li2B4O7 glass system

Transparent glasses in the system (100 − 3x)(Li2O–4B2O3)–x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) (where x = 10, 30 and 50, in molar ratio) embedded with nanocrystallites of SrBi2(Nb0.7V0.3)2O9 exhibited intense second harmonic signals in transmission mode when exposed to IR laser light at λ = 1064 nm. The second harmonic waves were found to undergo optical diffraction. The origin of optical diffraction in these samples was attributed to the self organised structures of fine crystallites of submicrometer size that were inscribed in-situ by the IR laser radiation. Laser Raman studies confirmed these crystallites to be vanadium doped strontium bismuth niobate

Optical diffraction of second harmonic generation in SrBi2(Nb0.7V0.3)2O9SrBi_2(Nb_{0.7}V_{0.3})_2O_9 in the SrO−Bi2O3−0.7Nb2O5−0.3V2O5–Li2B4O7SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5–Li_2B_4O_7 glass system

Transparent glasses in the system $(100-3x)(Li_2O–4B_2O_3)-x(SrO-Bi_2O_3-0.7Nb_2O_5-0.3V_2O_5)$ (where x = 10, 30 and 50, in molar ratio) embedded with nanocrystallites of $SrBi_2(Nb_{0.7}V_{0.3})_2O_9$ exhibited intense second harmonic signals in transmission mode when exposed to IR laser light at \lambda = 1064 nm. The second harmonic waves were found to undergo optical diffraction. The origin of optical diffraction in these samples was attributed to the self organised structures of fine crystallites of submicrometer size that were inscribed in-situ by the IR laser radiation. Laser Raman studies confirmed these crystallites to be vanadium doped strontium bismuth niobate