Glass Nanocrystal Composites Research Articles

Luminescence properties of CaMoO4 nanoparticles embedded borate composite glass

Transparent glasses of the 1.2CaO–0.2MoO3–B2O3 system were fabricated using the conventional melt-quenching technique. The glasses were heat-treated above the glass transition temperature (Tg) to yielded nanocrystalline composites of CaMoO4 (CMO) and CaB2O4 (CBO). The structural characterization of as-quenched and heat-treated glasses corroborated the crystallites of CaMoO4 and CaB2O4 using powder X-ray diffraction (XRD) and Raman spectroscopy. The various morphologies of the samples were studied using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Optical transmittance spectrum for as-quenched glass shows, approximately, 77% transparency (uncorrected for the reflection losses) from 2600 ​nm to 325 ​nm with a lower cut-off wavelength at 324 ​nm. The optical band gap (Eg) and refractive index (η) of the as-quenched transparent glass were found to be 3.43 ​eV and 1.615, respectively. Room-temperature photoluminescence properties of the as-quenched and glass nanocrystal composites (GNC) exhibit broad blue emission with UV excitation wavelengths (using laser and Xe lamp). Such distribution of CMO crystallites of nano-dimensions embedded in borate glass matrix could be used for various PL applications.

Enhanced second harmonic generation and photoluminescence in Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass

Non-linear optical properties and photoluminescence exhibited by Pr-doped LiNb0.5Ta0.5O3 nanocrystals embedded in a borate based glass are presented here. The glasses of composition 1.5Li2O–2B2O3–0.5Nb2O5–0.5Ta2O5:xPr6O11 (x = 0.0025, 0.005, and 0.01) were synthesized via the conventional melt-quenching technique, and the nanocrystal growth was induced by subjecting the as-quenched glasses to heat treatment between 530 and 560 °C for 3 h. Coalesced nanocrystals of sizes in the 20–38 nm range, resulting in the formation of dendritic spherulites, were obtained from the isothermal heat treatment. Effect of doping on the structural units of LiNb0.5Ta0.5O3 lattice was analysed by Raman studies, which indicated that Pr ions occupied Li+ vacancies or Nb/Ta antisites. A strong red emission at 620 nm, due to 1D2 → 3H4 electronic transition of Pr3+ ions, was observed upon excitation by a 450 nm radiation. The maximum intensity was exhibited by the composition corresponding to Pr-doping level, x = 0.005, while the crystallization had a pronounced effect on the intensity of the red output. A non-linear optical coefficient as high as 0.77 pm/V (twice that of d36 of potassium dihydrogen phosphate single crystal) was obtained from the bulk glass–nanocrystal composites of the composition in which x = 0.0025.

Lithium ion conductivity and dielectric relaxation in dendritic nanostructured LiTaO3 glass–nanocrystal composites

Lithium tantalate in single-crystalline and coarse-grained configurations is a poor ionic conductor and does not qualify as a solid electrolyte for lithium-based batteries. In this work, ionic conductivity was sought to be enhanced by the use of nanocrystals of LiTaO3 embedded in a borate-based glass matrix. Glasses of composition 3Li2O–4B2O3–Ta2O5 were formed by melt-quenching. The crystallization process was described by using isothermal crystallization kinetics, invoking the Johnson–Mehl–Avrami–Kolmogorov equation, which indicated a three-dimensional growth with an Avrami exponent of 3.5 and an effective activation energy for crystallization of 735 ± 65 kJ mol–1. Heat treatment of the as-quenched glasses was performed between 530 and 560 °C, and the evolution of LiTaO3 phase was studied by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The heat treatment yielded coalesced LiTaO3 nanocrystals of 18–32 nm size, forming dendritic structures in the glass matrix. Impedance analyses of the as-quenched and heat-treated glasses showed a dramatic improvement in dc conductivity (σdc), with a maximum around 3 × 10–3 S m−1 at 200 °C (σdcT = 1.5 S m−1 K) and activation energy of 0.54 eV for 530 °C/3 h heat-treated glasses. The values of σdc of the as-quenched glasses and of the 530 °C/3 h and 540 °C/3 h heat-treated glasses were about seven orders of magnitude higher than those of the single crystalline LiTaO3. Furthermore, the effect of heat treatment on lithium ion dynamics in the 40–200 °C temperature range was investigated by modulus formalism invoking the stretched exponential Kohlrausch–Williams–Watts function. The 7Li magic angle spinning NMR was used to investigate lithium self-diffusion in the nanostructured glass nanocrystal composites as a function of temperature between −10 °C and 60 °C.

Frequency and Temperature‐Independent Electrical Transport Properties of 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass‐Ceramics

The temperature (300–973 K) and frequency (100 Hz–10 MHz) response of the dielectric and impedance characteristics of 2BaO‐0.5Na2O–2.5Nb2O5–4.5B2O3 glasses and glass nanocrystal composites were studied. The dielectric constant of the glass was found to be almost independent of frequency (100 Hz–10 MHz) and temperature (300–600 K). The temperature coefficient of dielectric constant was 8 ± 3 ppm/K in the 300–600 K temperature range. The relaxation and conduction phenomena were rationalized using modulus formalism and universal AC conductivity exponential power law, respectively. The observed relaxation behavior was found to be thermally activated. The complex impedance data were fitted using the least square method. Dispersion of Barium Sodium Niobate (BNN) phase at nanoscale in a glass matrix resulted in the formation of space charge around crystal‐glass interface, leading to a high value of effective dielectric constant especially for the samples heat‐treated at higher temperatures. The fabricated glass nanocrystal composites exhibited P versus E hysteresis loops at room temperature and the remnant polarization (Pr) increased with the increase in crystallite size.

Evolution of Nanocrystalline Ba2NaNb5O15 in 2BaO–0.5Na2O–2.5Nb2O5–4.5B2O3 Glass System and Its Refractive Index and Band Gap Tunability

Monophasic Ba2NaNb5O15 was crystallized at nanometer scale (12-36 nm) in 2BaO-0.5Na(2)O-2.5Nb(2)O(5)- 4.5B(2)O(3) glass system. To begin with, optically transparent glasses, in this system, were fabricated via the conventional melt. quenching technique. The amorphous and glassy characteristics of the as-quenched samples were respectively confirmed by X-ray powder diffraction and differential thermal analyses. Nearly homogeneous distribution of Ba2NaNb5O15 (BNN) nanocrystals associated with tungsten bronze structure akin to their bulk parent structure was accomplished by subjecting the as-fabricated glasses to appropriate heat-treatment temperatures. Indeed transmission electron microscopy (TEM) carried out on these samples corroborated the presence of Ba2NaNb5O15 nanocrystals dispersed in a continuous glass matrix. The as-quenched glasses were similar to 75% transparent in the visible range of the electromagnetic spectrum. The optical band gap and refractive index were found to have crystallite size (at nanoscale) dependence. The optical band gap increased with the decrease in crystallite size. The refractive indices of the glass nanocrystal composites as determined by Brewster angle method were rationalized using different empirical models. The refractive index dispersion with wavelength of light was analyzed on the basis of the Sellmeier relations. At room temperature under UV excitation (355 nm) these glass nanocrystal composites displayed violet-blue emission which was ascribed to the defects states.

Mechanical properties of glasses and TiO2 nanocrystal glass composites in BaO–TiO2–B2O3 system

Glasses and glass-nanocrystal (anatase TiO2) composites in BaO–TiO2–B2O3 system were fabricated by conventional melt-quenching technique and controlled heat treatment respectively. Poisson's ratio and Young's moduli were predicted through Makishima–Mackenzie theoretical equation for the as-quenched glasses by taking the four and three coordinated borons into account. Mechanical properties of the glasses and glass-nanocrystal composites were investigated in detail through nanoindentation and microindentation studies. Predicted Young's moduli of glasses were found to be in reasonable agreement with nanoindentation measurements. Hardness and Young's modulus were enhanced with increasing volume fraction of nanocrystallites of TiO2 in glass matrix whereas fracture toughness was found susceptible to the surface features. The results were correlated to the structural units and nanocrystals present in the glasses.

Nanocrystallization of TiO2 Anatase Phase in Hydrophobic BaO–TiO2–B2O3 Glass System

Transparent colorless glasses in the ternary BaO–TiO2–B2O3 system were fabricated via conventional melt‐quenching technique. The glasses with certain molar concentrations of BaO and TiO2 on heat treatment at appropriate temperatures yielded nanocrystalline phase of TiO2 associated with the crystallite size in the 5–15 nm range. Nanocrystallized glasses exhibited high refractive index (n = 2.15) measured at λ = 543 nm. These glasses were found to be hydrophobic in nature associated with the contact angle of 90o. These high‐index glass nanocrystal composites would be of potential interest for optical device applications.

Crystallization of bismuth oxide nano-crystallites in a SiO2–PbO–Bi2O3 glass matrix

SiO2–PbO–Bi2O3 glasses having the composition of 35SiO2–xPbO–(65−x)Bi2O3 (where x=5, 20 and 45; in mol%) have been prepared using the conventional melting and annealing method. Differential scanning calorimetry (DSC) was employed to characterize the thermal behavior of the prepared glasses in order to determine their crystallization temperatures (Tcr). It has been found that Tcr decreases with the decrease of Bi2O3 content. The amorphous nature of the prepared glasses as well as the crystallinity of the produced glass–ceramics were confirmed by X-ray powder diffraction (XRD) analysis. SiPbBi2O6 glass nano-composites, comprising bismuth oxides nano-crystallites, were obtained by controlled heat-treatment of the glasses at their (Tcr) for 10h. Transmission electron microscopy (TEM) of the glass nano-crystal composites demonstrates the presence of cubic Bi2O3 nano-crystallites in the SiPbBi2O6 glass matrix. Nano-crystallites mean size has been determined from XRD line width analysis using Scherrer's equation as well as from TEM; and the sizes obtained from both analyses are in good agreement. These sizes varied from about 15 to 170nm depending on the chemical compositions of parent glasses and, consequently, their structure. Interestingly, replacement of the Bi2O3 by PbO in the glass compositions has pronounced effect on the nature, morphology and size of the formed nano-crystallites. Decrease of the Bi2O3 content increases the size of the nano-crystallites, and at the lowest Bi2O3 extreme, namely 20mol%, introduces minority of the monoclinic Bi2O4 in addition to the cubic Bi2O3. The crystallization mechanism is suggested to involve a diffusion controlled growth of the bismuth oxide nano-crystallites in the SiPbBi2O6 glass matrix with the zero nucleation rate.

Dielectric properties of (100−x)Li2B4O7–x(Ba5Li2Ti2Nb8O30) glasses and glass nanocrystal composites

Transparent glasses of various compositions in the system (100 -x)(Li2B4O7)-x(Ba5Li2Ti2Nb8O30) (5 <= x <= 20, in molar ratio) were fabricated by splat quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses (DTA). X-ray powder diffraction studies confirmed the as-quenched glasses to be amorphous and the heat-treated to be nanocrystalline. Controlled heat-treatment of the as-quenched glasses at 500 degrees C for 8 h yielded nanocrystallites embedded in the glass matrix. High Resolution Transmission Electron Microscopy (HRTEM) of these samples established the size of the crystallites to be in the nano-range and confirmed the phase to be that of Ba5Li2Ti2Nb8O30 (BLTN) which was, initially, identified by X-ray powder diffraction. The frequency, temperature and compositional dependence of the dielectric constant and the electrical conductivity of the glasses and glass nanocrystal composites were investigated in the 100 Hz to 10 MHz frequency range. Electrical relaxations were analyzed using the electric modulus formalisms. The imaginary part of electric modulus spectra was modeled using an approximate solution of Kohlrausch-Williams-Watts relation. The frequency dependent electrical conductivity was rationalized using Jonscher's power law. The activation energy associated with the dc conductivity was ascribed to the motion of Li+ ions in the glass matrix. The activation energy associated with dielectric relaxation was almost equal to that of the dc conductivity, indicating that the same species took part in both the processes. (C) 2010 Elsevier B.V. All rights reserved.

Optical and dielectric properties of transparent glasses and nanocrystals of lithium niobate and lithium diborate in borate glasses

The glass composition 92.5 Li 2 B 4 O 7 –7.5Nb 2 O 5 (mol%) was prepared by the conventional melt quenching technique. The as-quenched sample, blue and transparent, was heat-treated at 550 and 650 °C (HT). The glassy nature of the as-quenched sample was established by Differential scanning calorimetry (DSC). Lithium niobate LiNbO 3 and Li 2 B 4 O 7 nanocrystals were produced within the glass by heat-treating it at 550 and 650 °C/3. The amorphous nature of the as-quenched glasses and crystallinity of glass nanocrystal composites were confirmed by X-ray powder diffraction studies. Various optical parameters such as optical band gap ( E opt ) and Urbach energy (Δ E ) of these transparent glass–ceramics have been found to be crystallite size dependent. The volume ratio of the particles increases with increase in heat-treatment temperature. The behavior of the σ ac , with the increase in the heat-treatment (HT) temperature, was related with the decrease in the free ions number in the glass matrix and consequent increase in the fraction of the crystallites LiNbO 3 phase to the crystallites Li 2 B 4 O 7 phase and the glass matrix. The dielectric constants of the glass–ceramics decrease with increase in the HT temperature and with increase in frequency (0.12–100 kHz).

Structural and optical properties of (100−x)Li2B4O7·x(Ba5Li2Ti2Nb8O30) glasses and glass nanocrystal composites

Optically clear glasses of various compositions in the system (100-x)(Li₂B₄O₇)·x(Ba₅Li₂Ti₂Nb₈O₃₀) (5 ≤ x ≤ 20, in molar ratio) were fabricated by splat quenching technique. Controlled heat-treatment of the as-quenched glasses at 500 °C for 8 h yielded nanocrystallites embedded in the glass matrix. High Resolution Transmission Electron Microscopy (HRTEM) of these samples established the composition of the nano-crystallites to be that of Ba₅Li₂Ti₂Nb₈O₃₀. ¹¹B NMR studies revealed the transformation of BO₄ structural units into BO₃ units owing to the increase in TiO₆ and NbO₆ structural units as the composition of Ba₅Li₂Ti₂Nb₈O₃₀ increased in the glass. This, in turn, resulted in an increase in the density of the glasses. The influence of the nominal composition of the glasses and glass nanocrystal composites on optical band gap (E(opt)), Urbach energy (ΔE), refractive index (n), molar refraction (R(m)), optical polarizability (α(m)) and third order non-linear optical susceptibility (χ³) were studied.

Evolution of nanocrystalline BaBi2Nb2O9 in Li2B4O7–BaO–Bi2O3–Nb2O5 glass system

Transparent glasses and glass nano crystal composites (GNCs) of various compositions in the system (100−x)Li2B4O7–x(BaO–Bi2O3–Nb2O5) (where x=10, 20, and 30 in molar ratio) were fabricated via splat-quenching technique. The glassy nature of the as-quenched samples was established by differential thermal analyses. X-ray powder diffraction and transmission electron microscopic (TEM) studies confirmed the formation of layered perovskite BBN via a fluorite like phase. TEM studies revealed the presence of 10nm sized spherical crystallites of fluorite like BaBi2Nb2O9 phase in the glassy matrix of Li2B4O7 (LBO). The influence of composition on the dielectric and the optical properties (transmission, optical band gap) of these samples has been investigated.

Thermal, Structural, Optical, and Dielectric Properties of (100 − x)Li2B4O7 − x(BaO-Bi2O3-Nb2O5) Glasses and Glass-Nanocrystal Composites

Transparent glasses in the system (100 - x)Li2B4O7 - x(BaO-Bi2O3-Nb2O5) (x = 10, 20, and 30) were fabricated via the conventional melt-quenching technique. The amorphous and glassy characteristics of the as-quenched samples were established by the differential thermal analyses (DTA) and X-ray powder diffraction (XRD) studies. Glass-nanocrystal composites (GNCs) i.e., the glasses embedded with BaBi2Nb2O9 (BBN) nanocrystals (10-50 nm) were produced by heat-treating the as-quenched glasses at temperatures higher than 500 degrees C. Perovskite BBN phase formation through an intermediate fluorite-like phase in the glass matrix was confirmed via XRD and transmission electron microscopic (TEM) studies. The optical transmission properties of these GNCs were found to have a strong compositional (BBN content) dependence. The refractive index (n = 1.90) and optical polarizability (alphao = 15.3 x 10(-24) cm3) of the GNC (x = 30) were larger than those of as-quenched glasses. The temperature dependent dielectric constant (epsilonr) and loss factor (D) for the glasses and GNCs were determined in the 100-40 MHz frequency range. The epsilonr was found to increase with increase in heat-treatment temperatures, while the loss of the glass-nanocomposites was less than that of as-quenched glasses. The sample heat-treated at 620 degrees C/1 h (x = 30) exhibited relaxor behavior associated with a dielectric anomaly in the 150-250 degrees C temperature range. The frequency dependence of the dielectric maximum temperature was found to obey the Vogel-Fulcher relation (Ea = 0.32 eV and Tf = 201 K).

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

Transparent glasses in the system (100 − x) (Li2O − 2B2O3) − x (SrO − Bi2O3 − 0.7 Nb2O5 − 0.3 V2O5) (10 ≤ x ≤ 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 SrBi2(Nb0.7V0.3)2O9-δ (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 (Li2B4O7) reaching a value as high as ≈106 at 800 K. These glass nanocrystal composites were pyroelectric and ferroelectric at 300 K. Communicated by George W. Taylor

Electrical properties of SrBi 2(Nb 0.7V 0.3) 2O 9− δ in the SrO–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 cr) 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− δ (SBVN)) in lithium borate (Li 2B 4O 7 (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.

Nanocrystallization of Ferroelectric Strontium Bismuth Vanadium Niobate in Lithium Tetraborate Glasses

Transparent glass samples in (100-3x) (Li2O-2B2O3)-x(SrO-Bi2O3-0.7Nb2O5-0.3V2O5) (10 < or = x < or = 60, in molar ratio) system have been fabricated via conventional melt-quenching technique. The as-quenched samples, of all the compositions under study have been confirmed to be amorphous, by X-ray powder diffraction (XRD) studies. Differential thermal analysis (DTA) was employed to confirm the glassy nature of the as-quenched glasses. Glass composites comprising vanadium doped strontium bismuth niobate nanocrystallites were obtained by controlled heat-treatment of the as-quenched glasses at 783 K for 6 h. Perovskite SrBi2(Nb0.7VO3)2O9-delta phase formation was found to be preceded by an intermediate fluorite phase which was established via XRD and transmission electron microscopy (TEM). The dielectric constants (epsilonr) of the as-quenched glasses as well as the glass nanocrystal composites decreased with increase in frequency (100 Hz-10 kHz) at 300 K. Interestingly, the dielectric constant of the glass nanocrystal composite (heat-treated at 783 K/6 h) undergoes a maximum in the vicinity of the crystallization temperature of the host glass (Li2B4O7) reaching an anomalously high value (approximately 10(6)) at 800 K. Different dielectric mixture formulae were employed to rationalize the dielectric properties of the glass nanocrystal composite. The optical transmission properties of these glass nanocrystal composites were found to have strong compositional dependence.

Structural and optical properties of (100−x)(Li2B4O7)−x(SrO–Bi2O3–0.7Nb2O5–0.3V2O5) 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.

Study of microstructural behavior and nonadiabatic small polaron hopping conduction in BaTiO3 doped lead-vanadate glass and glass-ceramics dispersed with ferroelectric nanocrystals

Multicomponent semiconducting oxide glasses like (80 V2O5–20 PbO)+xBaTiO3 (x=5–30 wt %) dispersed with nanocrystalline BaTiO3 have been prepared by a fast quenching technique. Results of microstructural study and transport properties (between 80 and 450 K) of these glasses and some glass ceramics have been reported in this article. It has been shown from x-ray diffraction, scanning electron microscopic, and other studies that homogeneous glasses are formed with wide concentrations of BaTiO3 (x⩽30 wt %). Transmission electron microscopic study, however, indicates the presence of nanocrystalline phases in the glass matrix. Mott’s variable range (nonadiabatic) hopping conduction mechanism is found to be valid at the low temperature regime (below θD/4, θD being the Debye temperature) while in the high temperature regime (above θD/2), the polaron hopping models of Schnakenberg as well as Emin and co-workers can quantitatively predict the conductivity data for all these special types of multicomponent glass-nanocrystal composites. The model parameters, obtained from best fit of the experimental data with these models, are consistent with the glass compositions. The dielectric constants of these glasses are found to be very high (comparable to that of bulk BaTiO3) and about two orders of magnitude higher than those of BaTiO3 free (80 V2O5–20 PbO) and other transition metal oxide glasses. This novel character is considered to be due to the embedded nanocrystalline BaTiO3 phases. The glass samples annealed at 300 °C for 9 h in air also showed nano and microcrystalline BaTiO3 phase along with traces of PbV2O6, PbTiO3, TiO2, and Pb2V2O7 phases. Broad anomaly (with a maximum around 390 K) is observed from the thermal variation of dielectric constant data of these partially annealed glass-ceramic samples. This anomaly resembles to the anomaly observed around the Curie temperature (∼393 K) in bulk ferroelectric BaTiO3 crystal.

On the role of disclinations in relaxation and deformation processes in nanostructured materials

The features of grain boundary disclination splitting in nanocrystals are theoretically examined. It is shown that there are three basic variants of such splitting as a relaxation process which are specified by different values of elastic-energy decrease. Also, the contribution of disclinations as strengthening elements to processes of plastic deformation in metallic glass nanocrystal composites is discussed.

Disclinations and yield stress of metallic glass-nanocrystal composites

The relationship between anomalously high yield stress and structural features of metallic glass-nanocrystal composites, a new class of composite materials, is examined theoretically. It is shown, in particular, that the presence of disclination defects in nanocrystallites—elements of a composite—increases the yield stress of this glass-nanocrystal composite.