Synthetic Α-quartz Research Articles

Structure of the Room-Temperature 2.5 eV α-Quartz Single-Crystal Pulsed Cathodoluminescence Band

We study the room-temperature (RT) pulsed cathodoluminescence (PCL) spectrum of a high-purity synthetic α-quartz single crystal. The spectrum consists of two wide bands with intensity maxima at 415 and 490 nm (2.99 and 2.53 eV). The band at 490 nm (2.5 eV) is polarized in the XY crystal plane (perpendicular to the third-order symmetry axis) and possesses a structure with three peaks at 480±2, 487±2, and 493±2 nm (2.58±0.01, 2.55±0.01, and 2.52±0.01 eV). The intensities of the peaks at 480±2 and 493±2 nm increased with increase in the irradiation dose up to 45 kGy. Peaks are equidistant at the energetic scale. The energy separation between the peaks Δ = 0.03 ± 0.01 eV is equal in order of magnitude to energies of Li x O y molecular vibrations and to the energy of the optical phonon in α-quartz. We propose an explanation of the experimental data obtained. According to this explanation, the structure observed may be attributed to the amplitude modulation of the quartz 2.5 eV emission band by the crystalline electric fields on frequencies of optical phonons. The nonequilibrium phonons may arise during the electron-beam irradiation.

Hydrothermal Synthesis of Flower-Like α-Quartz Nanostructures from Iran Kaolin

Over the past many years, synthesized silica (SiO2) has attracted wide attention because of its unique characteristics, such as low density, low thermal conductivity, high surface area, high thermal shock resistance and high specific strength. In this study, Flower-like α-quartz nano-structures have been synthesized through the hydrothermal method. The synthetic α-quartz powder was obtained using the feedstock of locally kaolin after 15 h. reaction at 180°C. The characterization of the product was investigated using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Fourier Transform InfraRed (FT-IR) spectrometer. The FT-IR spectrum of the nano-crystalline powders confirms the presence of silica. SEM studies have revealed flower-like structures consisting of nano-sheets. In the synthetic quartz, most of the population is of nano-sized and lies between 1 µm to 15 µm. This developed method has many advantages such as synthesis at low temperature and desired pH to yield superior product of desired specification.

New E′ centers in neutron-irradiated α-quartz

Several E′-type defects have been revealed in neutron-irradiated natural and synthetic α-quartz by using electron paramagnetic resonance (EPR) spectroscopy. For the known center the primary spin Hamiltonian parameter matrices g and A(29Si) (hyperfine interaction with 29Si) have been refined and provide compelling evidence for spin trapping on the long-bond Si atom. The EPR spectra of the new center demonstrate that the super-hyperfine structure arises from the interaction with 27Al, the first-ever example of Al-associated E′ centers in crystalline quartz. The matrices g and A(29Si) of and another new center support the forward-oriented configuration proposed for the center in amorphous silica.

Triplet states of oxygen vacancy defects in α-quartz: Center

The paramagnetic center in triplet state occurring in electron-irradiated, synthetic α-quartz has been investigated by using electron paramagnetic resonance (EPR) spectroscopy. The primary spin Hamiltonian parameter matrices g, D and A (hyperfine interactions for five 29Si nuclei) have now been determined. The principal values and principal directions of D and A matrices allow us to suggest the structural model for this stable triplet defect. The center involves the two unpaired electrons located in the orbitals of two silicon atoms next to one oxygen vacancy each. Firm correlations between the spin Hamiltonian matrix principal axes and crystallographic directions have been attained.

Biradical states of oxygen-vacancy defects in α-quartz: centers $$ E_{2}^{\prime \prime } $$ and $$ E_{4}^{\prime \prime } $$

Several new radiation defects with total electron spin S = 1 occurring in electron-irradiated, synthetic α-quartz have been observed by using electron paramagnetic resonance spectroscopy. These defects are considered to be biradicals, i.e., pairs of S = 1/2 species. The concentration of these centers depends on the condition of the fast-electron irradiation. They have different decay behaviors that allow measurements of any individual species especially when it predominates over the others. The primary spin Hamiltonian parameter matrices g1, g2, D have now been determined for two similar defects, which herein are labeled \( E_{2}^{\prime \prime } \) and \( E_{4}^{\prime \prime } \). Inter-electron distances estimated by using the magnetic dipole model, suggest that the structures of centers \( E_{2}^{\prime \prime } \) and \( E_{4}^{\prime \prime } \) both involve the unpaired electrons each located in orbitals of two silicon atoms next to a common oxygen vacancy but which have slightly different Si–Si distances at 0.90 and 0.79 nm, respectively. This model is consistent with previous DFT calculations of the triplet configurations with local energetic minima. Observed decay behaviors suggest a transformation of centers \( E_{2,4}^{\prime \prime } \) to the analogous \( E_{1}^{\prime \prime } \) center. These triplet centers in quartz provide new insights into the structures of analogous defects in amorphous silica.

Elastic, anelastic, and piezoelectric coefficients of α-quartz determined by resonance ultrasound spectroscopy

All independent components of the elastic constants, internal friction, and piezoelectric coefficients of synthetic α-quartz have been simultaneously determined by resonance ultrasound spectroscopy coupled with laser-Doppler interferometry. Seventeen crystals obtained from Z and X regions with various infrared-absorption values were used; for each crystal, a complete set of the coefficients was determined using 72 resonance frequencies, which were measured by a needle-transducer tripod in a vacuum at a constant temperature with frequency-error limit of 0.001%. The infrared-absorption value and grown region did not strongly affect the material coefficients. Among the eight (elastic plus piezoelectric) coefficients, piezoelectric coefficients were significantly different from previously reported values. The six independent internal-friction components showed a positive correlation with the temperature derivatives of the corresponding elastic constants, indicating that the dominant damping mechanism was the phonon-phonon scattering. Our values at 30°C are C11=86.76GPa, C12=6.868GPa, C13=11.85GPa, C14=−18.02GPa, C33=105.5GPa, C44=58.14GPa, and e11=0.151C∕m2, and e14=−0.061C∕m2.

Cathodoluminescence and epitaxy after sequential Rb- and Ge-ion implantation in α-quartz

The luminescence properties of ion-beam doped silica and quartz sensitively depend on the ion species and fluence and the thermal processing during or after ion implantation. While no epitaxy, but a high cathodoluminescence (CL) output can be reached after dynamic Ge-ion implantation in quartz, full planar epitaxy is achieved after alkali-ion implantation (Na, Rb, Cs) under appropriate ion and annealing conditions. Now for the first time we achieved high luminescence intensity and (partial) recrystallization of α-quartz by double Ge/Rb-ion implantation. Pure synthetic α-quartz samples were irradiated with 175keV Rb-ions and subsequently with 120keV Ge-ions and post-annealed at 1170K in vacuo, air or 18O2 gas. A comparative analysis of the epitaxy (via RBS-Channeling) and cathodoluminescence was carried out, the latter showing three dominant emission bands in the blue/violet region at 2.95, 3.25 and 3.53eV, which were assigned to Rb- or Ge-implantation. For increasing CL temperature, a shift of the predominant peak from 2.95 to 3.25eV was noted after air-annealing, accompanying partial chemical epitaxy.

Achieving epitaxy and intense luminescence in Ge∕Rb-implanted α-quartz

The luminescence properties of ion-beam doped silica and quartz depend sensitively on the ion species and fluence and the thermal processing during and after ion implantation. In an attempt to achieve high luminescence intensity and full planar recrystallization of α-quartz, we studied double Ge∕Rb-ion implantation, where the Rb ions serve as a catalyst only. Synthetic α-quartz samples were irradiated with 175 keV Rb ions and subsequently with 120 keV Ge ions with fluences of 1×1014–1×1016ions∕cm2 and postannealed at 1170 K in air. A comparative analysis of the epitaxy, migration of the implanted ions, and cathodoluminescence (CL) were carried out. The CL spectra exhibit three strong emission bands in the blue/violet range at 2.95, 3.25, and 3.53 eV, which were assigned to Rb- and/or Ge-related defect centers. For up to 1015 implanted Geions∕cm2, large fraction (75%) of the Ge atoms reach substitutional Si sites after the epitaxy.

Comparison of acoustic properties between natural and synthetic α-quartz crystals

Accurate measurements of bulk and leaky surface acoustic wave (LSAW) velocities of natural α-quartz crystal were carried out using the line-focus-beam and plane-wave ultrasonic material characterization systems and then these measured velocities were compared with the velocities of synthetic α-quartz crystals. Longitudinal velocities of principal X-, Y-, and Z-cut specimens; shear velocities with X-axis polarized particle displacements of the Y- and Z-cut specimens; and LSAW velocities for these three specimens were precisely measured. We found all the velocities for the bulk waves and the LSAWs of natural quartz to be slightly smaller (within 1.00 m/s) than the velocities of synthetic quartz. Therefore, the acoustical physical constants of the natural quartz are very similar to those of synthetic quartz we reported recently.

Measurements of bulk acoustic properties of syntheticα-quartz

A preliminary study of the acoustical physical constants (elastic constant, piezoelectric constant, dielectric constant, and density) of commercially available, synthetic α-quartz has been conducted which involved the accurate measurement of the longitudinal velocities and densities for X-, Y-, and Z-cut specimens. Significant differences in longitudinal velocity exceeding 0.5%, especially along the Z-axis of propagation, were observed between the measured longitudinal velocities and the calculated velocities using the constants published by Mason or Bechmann et al. Research directions into accurately determining all the acoustical physical constants are suggested.

Characterization of vacancies in as-grown and electron irradiated α-quartz by means of positron annihilation

Synthetic α-quartz is shown to contain a significant concentration (several ppm) of vacancies. The major concentration of vacancies is suggested to be in the form of divacancies, giving rise to a positron lifetime of 285±5 ps, but in addition, there is a much smaller concentration of large vacancy clusters that are observable only after electron irradiation, whereupon they give rise to a positron lifetime close to 425 ps. Annealing between 900 and 1000 °C causes disappearance of divacancies and formation of vacancy clusters giving rise to a positron lifetime close to 300 ps. Above ∼950 °C positronium is formed with an exceptionally long lifetime (3–5 ns) ascribable to the formation of an amorphous phase connected with the thermal instability of β-quartz. Electron irradiation (2.3 MeV at 8 °C) gave rise to a 250±5 ps lifetime component interpreted to signify formation of neutral monovacancies, V0 and/or VSi. Their introduction rate is nonlinear, decreasing abruptly by a factor of ∼5 above a dose of 1×1017 e/cm2, an effect which is ascribed to the removal of irradiation-produced vacancy-interstitial complexes by means of electron-hole recombination during the irradiation.

Haven ratio for sodium in synthetic α-quartz

physica status solidi (a)Volume 80, Issue 1 p. K15-K20 Short Note Haven ratio for sodium in synthetic α-quartz† H. Jain, H. Jain Department of Nuclear Energy, Brookhaven National Laboratory, Upton Search for more papers by this author H. Jain, H. Jain Department of Nuclear Energy, Brookhaven National Laboratory, Upton Search for more papers by this author First published: 16 November 1983 https://doi.org/10.1002/pssa.2210800149Citations: 2 † Part of this work was carried out at Argonne National Laboratory. ‡ Upton, Long Island, New York 11973, USA. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume80, Issue116 November 1983Pages K15-K20 RelatedInformation

Lattice Image Analysis of the Metamict Transformation in Synthetic Quartz

The irradiation-induced crystalline-to-amorphous transformation in quartz and other silicates has been investigated because of its importance to nuclear waste storage ard frequency control. The transformation to an amorphous (metamict) state is accompanied by up to 14% decrease in density.Recent in-situ electron damage studies of synthetic α-quartz using transmission electron microscopy have shown that the metamict transformation occurs in two stages at different rates: first, a rapid, heterogeneous nucleation of well-defined amorphous inclusions; and second, a more gradual, homogeneous loss of correlation in the surrounding matrix. The first stage initiates at doses less than ten times the second. Experiments at different electron energies have established that both stages can result from the ionizing component of the radiation alone. The proposed radiolytic damage mechanism involves localization of excitations resulting in bond breakage which provides the necessary topological freedom for reorientation of SiO4 tetrahedra. Water has been implicated in the first-stage heterogeneous nucleation.

Anomalous hyperfine splitting of 57Fe in α-quartz

The hyperfine splitting of 57Fe for substitutional Fe 3+ in synthetic α-quartz was found to increase monotonically with increasing slope of the fine structure transitions exceeding the free ion value several times in highly anisotropic regions. A tentative explanation for this hitherto unreported effect is proposed.

Deformation and fracture of synthetic ?-quartz

The deformation and fracture properties of synthetic α-quartz crystals were measured using hardness, pre-cracked bend and Hertzian tests over the range 20 to 545° C in air and dry nitrogen. The resistance to fracture decreases significantly with increase in temperature and is orientation-dependent (becoming very small as the inversion temperature is approached), while the microhardness remains relatively insensitive to temperature and environment. These effects are interpreted in terms of the moisture content of the environment and the intrinsic water content of the crystals.

EPR study of substitutional-aluminum-related hole centers in synthetic α-quartz

The analysis of the anisotropic EPR spectra at 77°K of three unstable paramagnetic centers with 27Al hyperfine structure in x-irradiated a-quartz is presented. These centers are described by models in which a hole is localized in a nonbonding orbital of an oxygen which is adjacent to an aluminum impurity in a silicon lattice site; there is an interstitial ion H +, Na +, or Li + associated with this configuration. The structure of these centers is related to the stable compensator-free substitutional-aluminum center reported by Griffiths, Owen, and Ward. Two additional unstable centers with 27Al hyperfine structure, which are observed at lower concentrations after x-irradiation at 77°K, are reported; one of these centers is a second species with H +-compensation while the other is apparently another compensator-free center. The EPR spectra of quartz plates grown on a major rhombohedral seed show a strong nonrandomness in the distribution of aluminum among the three silicon sites of the unit cell. The preferred site was determined by relating the angular dependence of the spectra to the atomic arrangement in the sample. Using the identification of this site, the directions of the principal EPR interactions were related directly to the bond directions at the paramagnetic center.

The 3000–3900 cm −1 absorption bands and anelasticity in crystalline α-quartz

Studies are reported of the 3000–3900 cm −1 absorption spectra of natural and synthetic α-quartz at ∼77°K and of the 5 mc anelastic loss peak near 100°C. The absorption spectra of natural quartz samples before and after various treatments are in general agreement with those reported by other workers and the conclusions based on absorption results are consistent with those derived from the acoustic studies. The behavior of synthetic quartz, presumably because of other defect structures and the presence of more numerous and extensive disordered regions, varies in some respects. The data indicate that, in contrast to natural quartz, Li + incorporated during growth of synthetic quartz enters sites which are different from those involved when Li + is introduced by electrodiffusion. Furthermore, for a crystal which had been rapidly grown in a Li-Al doped NaOH solution, the data signify more alkali near the edge and more bonded OH near the seed. The absorption characteristics before and after heat treatment of a rapidly grown synthetic show that the inclusions causing milkiness contain ordered water. Moreover, the good correlation found between anelastic loss and extinction coefficient is interpreted to mean that the high temperature relaxation peak is due to hydrogen bonded OH and not to an aluminum silicate as postulated previously.