Anti-glass Phases Research Articles

Crystallization in the TeO2 - Ta2O5 - Bi2O3 system: From glass to anti-glass to transparent ceramic

Glass samples belonging the TeO2 - Ta2O5 - Bi2O3 (TTB) system are prepared by conventional melt-quenching technique and the corresponding vitreous domain is identified. A crystallization study of the 80 TeO2 - 10 Ta2O5 - 10 Bi2O3 glass composition versus temperature shows structural transitions from glass to the stabilization of an unreported translucent anti-glass phase and eventually to a fully transparent crystalline ceramic in both the visible and infrared ranges. The structure and microstructure of the anti-glass and ceramic phases are characterized by Powder X-Ray Diffraction, Electron Back-Scatter Diffraction, Transmission Electron Microscopy and Raman spectroscopy. The optical properties of undoped and Er3+-doped transparent samples are also discussed. Up-conversion green emission band shows that the glass intensity is about 2 and 4 times more intense than that of the anti-glass and the ceramic, respectively. Furthermore, a large spectral bandwidth of 105 nm is found in the anti-glass sample. The advantageous spectroscopic characteristics found here, together with the good thermal stability of these samples, suggest that the anti-glass phase has potential applications as amplification medium for the generation of ultrashort (femtoseconds) pulses.

Neutron diffraction investigation of strontium tellurite glass, anti-glass and crystalline phases

ABSTRACT Neutron diffraction studies were performed on xSrO-(100-x)TeO2 (x = 5, 7.5 and 10 mol%) glass, anti-glass and crystalline samples. For the structural modeling, Fourier transformation, Reverse Monte Carlo (RMC) simulations and Rietveld refinement were used. The pair distribution functions show the nearest neighbor peaks of Sr—O, Te—O and O—O correlations at 2.64, 1.95 and 2.70 Å, respectively. RMC analysis was used to determine the partial pair distributions, cation-oxygen bond lengths, co-ordination numbers and three-particle bond-angle distributions. The glass sample with 7.5 mol% SrO was transformed into the anti-glass phases by annealing at 350°C and into the crystalline phases by annealing of the anti-glass sample at 450°C. The crystal structure parameters of the anti-glass and crystalline samples were determined by Rietveld analysis and it was found that the anti-glass sample contains disordered SrTe5O11 and SrTeO3 phases, while the crystalline sample contains monoclinic SrTeO3 and orthorhombic TeO2 phases.

Photoluminescence and thermal properties of trivalent ion-doped lanthanum tellurite anti-glass and glass composite samples

Transparent glass-ceramic samples of lanthanum tellurite system: xR2O3–5La2O3-(95-x)TeO2 (x = 0 and 1 mol% and R = Sm, Eu, Gd, Dy, Er, Yb and B) were synthesized by melt quenching technique. The pure and rare-earth-ion doped lanthanum tellurite samples contain triangular, rectangular, spherical and flower-shaped micro-inclusions (droplets) of anti-glass phases that co-exist with the glassy matrix. The anti-glass phase possesses the long-range order of cations (La, Te and rare-earth ions) but exhibits vibrational disorder due to random arrangements of the anions (oxygens). The average size of the anti-glass droplets increases significantly with the addition of rare-earth ions, while the addition of 1-mol% B2O3 completely suppresses the growth of the anti-glass inclusions. The rare-earth ions decrease the thermal stability and glass-forming ability (GFA) of the lanthanum tellurite samples but B2O3 enhances thermal stability and GFA while it reduces the photoluminescence (PL) intensity. The Raman spectra of the co-existing glass and anti-glass phases in all the glass-ceramic samples are very similar and show broad bands that are characteristic of the disordered phase. The PL spectra of rare-earth-doped lanthanum tellurite samples were measured at different excitation and emission wavelengths and the lanthanum tellurite samples produce strong white light emission on doping with Gd, Dy or Yb.

Structural, thermal and optical characterization of co-existing glass and anti-glass phases of xLa2O3-(100-x)TeO2 and 2TiO2-xLa2O3-(98-x)TeO2 systems

Glass-ceramic, anti-glass and crystalline samples of two systems: xLa2O3-(100-x)TeO2 (x = 5, 7, 10, 12.5, 15 and 20 mol%) and 2TiO2-xLa2O3-(98-x)TeO2 (x = 5, 7 and 10 mol%) were prepared by melt quenching. Glass-ceramic samples are transparent and contain co-existing glass and anti-glass inclusions. Samples with La2O3 concentration greater than 10 mol% required more rapid splat quenching to prepare transparent glass-ceramics whereas the sample with 20 mol% La2O3 produces crystalline monoclinic La2Te4O11 by slow melt quenching and disordered anti-glass phase with the structure of cubic La2Te6O15 by splat quenching. The addition of TiO2 in xLa2O3-(100-x)TeO2 system reduces the size of the inclusions, but it enhances their concentration and also increases the optical transparency and thermal stability of the glasses. Micro-Raman studies found that the Te—O coordination number decreases with an increase in La2O3 mol% and the co-existing glass and anti-glass phases have the same value of average Te—O speciation.

A comprehensive study of the glass/translucent anti-glass/transparent ceramic structural ordering in the Bi2O3[sbnd]Nb2O5–TeO2 system

The full and congruent crystallization of the Bi0.8Nb0.8Te2.4O8 (BNT) glass leads to perfectly transparent ceramic in both the visible and near infrared ranges. While heating the parent glass, an intermediate structural regime order – called anti-glass – that shows chemical inhomogeneity at the nanometer scale and with a long-range cationic ordering while retaining a strong local anionic disorder is observed. Here, we report on the crystallization sequence starting from the Bi0.8Nb0.8Te2.4O8 glass system and show that an intermediate Bi0.8Nb0.8Te2.4O8 anti-glass phase (polymorph 1) is first formed, before transforming into a more ordered and ceramic material (polymorph 2). In particular, we provide a comprehensive structural study of the crossover between glass and its crystalline counterpart through intermediate steps. Similarities and differences between the structures, microstructures of Bi0.8Nb0.8Te2.4O8 glass, anti-glass and ceramic materials of identical composition are investigated in details at different length scales by X-ray and neutron powder diffraction, SEM-EBSD, TEM, NMR and Raman spectroscopy. The optical properties of the anti-glass and ceramic are discussed in correlation with the structure and microstructure observations. This study paves the way for understanding the complex mechanisms at the origin of the full and congruent crystallization from the parent glass.

Structure of strontium tellurite glass, anti-glass and crystalline phases by high-energy X-ray diffraction, reverse Monte Carlo and Rietveld analysis.

The structures of xSrO-(100 - x)TeO2 (x = 5, 7.5, 8.5 and 10 mol.%) glass, anti-glass and crystalline samples were studied by high-energy X-ray diffraction (HEXRD), reverse Monte Carlo (RMC) simulations, atomic pair distribution function analysis and Fullprof Rietveld refinement. The atomic pair distributions show the first peak at 1.90 Å due to the Te-O equatorial bonds and the Te-O peak is asymmetrical due to the range of Te-O bond lengths in glass, anti-glass and crystalline samples. The short-range structural properties of glasses such as Te-O bond lengths, Te-O speciation, Te-Te distances and O-Te-O bond angle distributions were determined by RMC simulations. The average Te-O coordination number (NTe-O) for 5SrO-95TeO2 glass is 3.93 which decreases to 3.59 on increasing the SrO concentration to 10 mol.%. The changes in NTe-O revealed that the glass network predominantly contains TeO4 units with a small amount of TeO3 units and there is a structural transformation TeO4 → TeO3 with an increase in SrO concentration. The O-Te-O bond angle distributions have a peak at 79° and reveal that the Oequatorial-Te-Oequatorial bonds are the most abundant linkages in the tellurite network. Two glass samples containing 7.5 and 8.5 mol.% of SrO were annealed at 350°C for 1 h to produce anti-glass phases; they were further annealed at 450°C for 4 h to transform them into crystalline phases. The anti-glass samples are disordered cubic SrTe5O11 and the disordered monoclinic SrTeO3 phases, whereas the crystalline samples contain monoclinic SrTeO3 and the orthorhombic TeO2 phases. The unit-cell parameters of the anti-glass and crystalline structures were determined by Fullprof Rietveld refinement. Thermal studies found that the glass transition temperature increases with an increase in SrO mol.% and the results on the short-range structure of glasses from Raman spectroscopy are in agreement with the RMC findings.

Highly Transparent Fluorotellurite Glass-Ceramics: Structural Investigations and Luminescence Properties.

Crystallization from glass can lead to the stabilization of metastable crystalline phases, which offers an interesting way to unveil novel compounds and control the optical properties of resulting glass-ceramics. Here, we report on a crystallization study of the ZrF4-TeO2 glass system and show that under specific synthesis conditions, a previously unreported Te0.47Zr0.53OxFy zirconium oxyfluorotellurite antiglass phase can be selectively crystallized at the nanometric scale within the 65TeO2-35ZrF4 amorphous matrix. This leads to highly transparent glass-ceramics in both the visible and near-infrared ranges. Under longer heat treatment, the stable cubic ZrTe3O8 phase crystallizes in addition to the previous unreported antiglass phase. The structure, microstructure, and optical properties of 65TeO2-35ZrF4Tm3+-doped glass-ceramics, were investigated in detail by means of X-ray diffraction, scanning and transmission electron microscopies, and 19F, 91Zr, and 125Te NMR, Raman, and photoluminescence spectroscopies. The crystal chemistry study of several single crystals samples by X-ray diffraction evidence that the novel phase, derived from α-UO3 type, corresponds in terms of long-range ordering inside this basic hexagonal/trigonal disordered phase (antiglass) to a complex series of modulated microphases rather than a stoichiometric compound with various superstructures analogous to those observed in the UO3-U3O8 subsystem. These results highlight the peculiar disorder-order phenomenon occurring in tellurite materials.

Effects of doping of trivalent ions on glass and anti-glass phases of Bi2O3-Nb2O5-TeO2 system

The effects of addition of trivalent metal oxides: Gd2O3, Dy2O3, Eu2O3, Er2O3, Y2O3, and B2O3 on the size and distribution of anti-glass phases of BiNbTe2O8 in the system: xR2O3-(10-x)Bi2O3-10Nb2O5-80TeO2 (x = 1 and 2 mol%) are studied. The samples prepared by melt-quenching are predominantly glassy phase but contain co-existing inclusions (droplets) of anti-glass BiNbTe2O8. The incorporation of Gd2O3, Dy2O3, Eu2O3, Er2O3, and Y2O3 in the glass system enhances the glass transition temperature and promotes the growth of the anti-glass droplets. On the other hand the addition of B2O3 decreases the glass transition temperature and inhibits the growth of the inclusions and produces purely amorphous samples. The photoluminescence spectra show intense red emission in Eu3+-doped samples while yellow light is emitted from Dy3+ doped samples. The micro-Raman spectra of the glass and anti-glass inclusions are very similar which indicates same chemical composition and short-range structure of the glass and anti-glass phases.

Structural, optical and thermal properties of glass and anti-glass phases in strontium tellurite and borotellurite systems doped with europium

Glass sample of the composition: 10SrO-90TeO2 was prepared by melt-quenching technique and found to contain triangular, rectangular, and spherical shaped micro-inclusions of the average size ∼803 μm in the glassy matrix. The inclusions grow to an average size of ∼1347 μm and assume flower-like morphology upon adding 1 mol% Eu2O3 in the 10SrO-90TeO2 sample. X-ray diffraction studies showed that the micro-inclusions exhibit sharp peaks, but their Raman spectra have broad phonon bands that are indistinguishable or very similar to that of the glassy matrix phase. The addition of 10 mol% B2O3 in the samples inhibits the growth of inclusions of anti-glass phases and forms purely amorphous samples. B2O3 significantly enhances the photoluminescence properties of Eu3+ doped samples. Furthermore, B2O3 converts the four-fold co-ordinated Te-O structural units into three-fold co-ordinated Te-O units.

Glass and anti-glass phase co-existence and structural transitions in bismuth tellurite and bismuth niobium tellurite systems

Glass and anti-glass samples of Bi2O3-TeO2 and Bi2O3-Nb2O5-TeO2 were prepared by ice-water quenching and normal-quenching respectively. The bismuth tellurite system has poor glass forming ability (GFA) and forms a glassy phase at low Bi2O3 concentration of 2 to 5-mol%. On increasing Bi2O3 concentration to 10mol%, a mixture of glass and anti-glass phases are formed by rapid quenching of the melt. A further increase in Bi2O3 concentration to 20mol%, produces a sample consisting of entirely Bi2Te4O11 anti-glass upon melt-quenching. An anti-glass is a solid, which has long range order of cations (Te4+, Bi3+, Nb5+ etc.) but these are statistically distributed at their sites while the anion sites are partially vacant. Consequently the X-ray diffraction (XRD) patterns of bismuth tellurite and bismuth niobium tellurite anti-glass samples show sharp XRD peaks but the Raman spectra show broad phonon bands due to disturbed short-range order of the anions. The addition of Nb2O5 to the Bi2O3-TeO2 system significantly enhances the GFA. Samples from the system: xBi2O3-xNb2O5-(100-2x)TeO2 grow micro-inclusions or spherulites of size of several micron within the glass matrix on slow melt-cooling. Heat treatment of 7.5Bi2O3-7.5Nb2O5-85TeO2 sample show structural transitions from glass→anti-glass→crystalline phases.

Controllable quantum spin glasses with magnetic impurities embedded in quantum solids

Magnetic impurities embedded in inert solids can exhibit long coherence times and interact with one another via their intrinsic anisotropic dipolar interaction. We argue that, as a consequence of these properties, disordered ensembles of magnetic impurities provide an effective platform for realizing a controllable, tunable version of the dipolar quantum spin glass seen in LiHo$_x$Y$_{1-x}$F$_4$. Specifically, we propose and analyze a system composed of dysprosium atoms embedded in solid helium. We describe the phase diagram of the system and discuss the realizability and detectability of the quantum spin glass and antiglass phases.

ChemInform Abstract: Collective Phenomena in the LiHoxY1‐xF4 Quantum Ising Magnet: Recent Progress and Open Questions

AbstractReview: 83 refs.

Unreachable glass transition in dilute dipolar magnet

In magnetic systems the combined effects of disorder and frustration may cause the moments to freeze into a disordered state at a spin-glass transition. Recent experiments have shown that the rare earth compound LiHo(0.045)Y(0.955)F(4) freezes, but that the transition is unreachable because of dynamics that are 10(7) times slower than in ordinary spin-glass materials. This conclusion refutes earlier investigations reporting a speed-up of the dynamics into an exotic anti-glass phase caused by entanglement of quantum dipoles. Here we present a theory, backed by numerical simulations, which describes the material in terms of classical dipoles governed by Glauber dynamics. The dipoles freeze and we find that the ultra-slow dynamics are caused by rare, strongly ordered clusters, which give rise to a previously predicted, but hitherto unobserved, Griffths phase between the paramagnetic and spin-glass phases. In addition, the hyperfine interaction creates a high energy barrier to flipping the electronic spin, resulting in a clear signature in the dynamic correlation function.

Collective Phenomena in the LiHoxY1−xF4 Quantum Ising Magnet: Recent Progress and Open Questions

In LiHoxY1−xF4, the magnetic Holmium Ho3+ ions behave as effective Ising spins that can point parallel or antiparallel to the crystalline c-axis. The predominant inter-Ho3+ interaction is dipolar, while the Y3+ ions are non-magnetic. The application of a magnetic field Bx transverse to the c-axis Ising direction leads to quantum spin-flip fluctuations, making this material a rare physical realization of the celebrated transverse field Ising model. The problems of classical and transverse-field-induced quantum phase transitions in LiHoxY1−xF4 in the dipolar ferromagnetic (x = 1), diluted ferromagnetic (0.25 ≲ x < 1) and highly diluted x ≲ 0.25 dipolar spin glass regimes have attracted much experimental and theoretical interest over the past twenty-five years. Two questions have received particular attention: (i) is there an antiglass (quantum disordered) phase at low Ho3+ concentration and (ii) what is the mechanism responsible for the fast Bx-induced destruction of the ferromagnetic (0.25 ≲ x < 1) and spin glass (x ≲ 0.25) phases? This paper reviews some of the recent theoretical and experimental progress in our understanding of the collective phenomena at play in LiHoxY1−xF4, in both zero and nonzero Bx.

The quantum efficiency of broad-band emitting Cr(III)-doped luminescent materials

Chromium(III)-doped luminescent materials can have high efficiency when crystalline. As glass, however, their efficiency is low to vanishing. This point is discussed using recent data on chromium-doped yttrium-stabilized ZrO 2 which is an anti-glass phase. Spectroscopically it is in between a glass and a crystalline material.

Luminescence and energy transfer in europium Tellurite anti-glass phases

The luminescence and energy transfer properties of two lower symmetrical europium tellurite anti-glass phases are reported, viz. Eu 1.79TeO x , which has a pseudo-tetragonal structure, and Eu 1.08TeO x , which has a monoclinic ordered crystal structure. In the pseudo-tetragonal phase the Eu 3+ ions occupy two major types of sites. In the monoclinic phase there are at least seven different crystallographic sites available to the Eu 3+ ions. At low temperatures transfer of excitation energy to the sites with the lowest 5D 0 energy levels occurs, and only these sites luminesce. Above 10 K backtransfer to higher 5D 0 levels takes place. The energy migration process, which becomes important at temperatures above 20 K for the pseudo-tetragonal phase and above 10 K for the monoclinic phase, is two-phonon assisted. For both compounds the assistance mechanism up to about 50 K is two-site non-resonant, and at higher temperatures it is one-site resonant.

Formation and luminescence of lower symmetrical tellurite anti-glass phases

Two series of nonstoichiometric lanthanoid tellurite phases have been identified which are similar to cubic ( Ln,Te)O n anti-glass phases with CaF 2 defect structure. Their X-ray diagrams indicate low-symmetrical CaF 2 superstructures. Monoclinic (or pseudotetragonal) subcells were determined. Anti-glass disorder is consistent with the Eu 2+ and Te 4+ luminescence of one series, but can be excluded for the other one.

Luminescence of tellurite anti-glass phases

The luminescence of two series of anti-glass tellurites of La, Gd, and Y, one Te-rich and the other lanthanide-rich, are reported. It is the first example of an oxidic system with high Te 4+ concentration which shows luminescence. The thermal quenching temperature is low (∼100 K). As far as possible the results are discussed in terms of the strongly disordered nature of these compositions.

Anti-glass phases and other lanthanide tellurates with fluorite-related structures

Two series of metastable, cubic face-centered non-stoichiometric anti-glass tellurates of Y, La, and lanthanides have been found: Te-richer phases, containing tetravalent Te only, with compositions between Ln 2Te 6O 15 and Ln 4Te 7O 20 and lattice constants of 570−549 pm, and Ln-richer phases containing minor amounts of hexavalent Te, with Ln:Te ratios between 3:2 and 11:10, and lattice constants between 574 and 539 pm.