Channel constituents in synthetic beryl: ammonium (original) (raw)
Related papers
STATE OF MOLECULES AND IONS IN THE STRUCTURAL CHANNELS OF SYNTHETIC BERYL WITH AN AMMONIUM IMPURITY
The contents of the structural channels of beryl, grown hydrothermally from an ammonium-containing solution, were investigated by IR and EPR spectroscopy. Using IR spectroscopy we found that water molecules, ammonium ions, and a small number of HCl molecules enter the structural channels of beryl in the course of mineral growth. In these beryls, the ammonium ions play the role of alkali cations. The ammonium ions are as rigidly fixed in the lattice as are water molecules; they are eliminated by calcination at high temperatures close to the decomposition temperature. On exposure to radiation at 77 K, the paramagnetic NH3 and H0 radicals are stabilized in the structural channels of beryl. In addition to the known H0 radical, other states of atomic hydrogen, interacting with medium protons, are observed as well. For one of the additional radicals, Hb, we suggest the model of atomic hydrogen stabilized at the center of a silicon-oxygen ring with two water molecules in adjacent cavities.
FTIR spectroscopy of D2O and HDO molecules in the c-axis channels of synthetic beryl
This paper presents the results of Fourier transform infrared (FTIR) spectroscopy of a synthetic beryl, containing D2O molecules in its c-axis channels, which we synthesized under hydrothermal conditions at 600 °C and 1.5 kbar. The frequencies of absorbance bands in the range of the stretching vibrations and their overtones and combination modes for D2O and HDO molecules have been assigned for the first time. On the basis of our assignments, the absorbance bands observed for the natural beryl in the range of the OD stretching vibrations have been explained. Note! Unfortunately during publication's processing Greek letters ν and δ were unintentionally transformed into Latin letters 'n' and 'd', respectively. Also symbol 'perpendicular' was transformed to ^.
Hydrothermal Synthetic Red Beryl from the Institute of Crystallography, Moscow
Gems & Gemology, 2001
The beryl crystal structure contains two different sites along "open" channels that can incorporate water molecules (Schaller et al., 1962; Wood and Nassau, 1968; Schmetzer, 1989; Deer et al., 1997). These variations in transition metal, alkali element, and water contents in beryls cause differences in physical properties (such as refractive index, specific gravity, and color), as well as in visible and infrared absorption spectra. Natural Red Beryl. Gem-quality red beryl occurs at a single locality in the Wah Wah Mountains of southern Utah (see, e.g., Flamini et al., 1983;
Atomic resolution imaging of beryl: an investigation of the nano-channel occupation
Journal of Microscopy, 2017
Beryl in different varieties (emerald, aquamarine, heliodor etc.) displays a wide range of colours that have fascinated humans throughout history. Beryl is a hexagonal cyclo-silicate (ring-silicate) with channels going through the crystal along the c-axis. The channels are about 0.5 nm in diameter and can be occupied by water and alkali ions. Pure beryl (Be 3 Al 2 Si 6 O 18) is colourless (variety goshenite). The characteristic colours are believed to be mainly generated through substitutions with metal atoms in the lattice. Which atoms that are substituted is still debated it has been proposed that metal ions may also be enclosed in the channels and that this can also contribute to the crystal colouring. So far spectroscopy studies have not been able to fully answer this. Here we present the first experiments using atomic resolution scanning transmission electron microscope imaging (STEM) to investigate the channel occupation in beryl. We present images of a natural beryl crystal (variety heliodor) from the Bin Thuan Province in Vietnam. The channel occupation can be visualized. Based on the image contrast in combination with ex situ element analysis we suggest that some or all of the atoms that are visible in the channels are Fe ions.
Optical Properties of Natural and Synthetic Beryl Crystals
IOP Conference Series: Materials Science and Engineering, 2015
The results of investigation of photoluminescence and UV-Visible absorption spectra of natural beryl crystals from Ural Mountains before and after fast neutron irradiation and synthetic crystal grown in Belarus and Russia are presented. Photoluminescence (PL) spectra of synthetic beryl crystals contain a broad band with maxima 740 nm excited both by UV light (λex = 260 nm, 271 nm) and laser excitation (λex =263 nm). This band is connected with Fe 2+ ions. The temperature lowering down to 8 K leads to appearance of narrow lines in the 680 -720 nm regions. Emission lines observed in the luminescence spectra are connected with electron transition 2 Eg→ 4 A2g of the Cr 3+ ions: R-lines (682.5 nm) arise from isolated Cr 3+ ions occupying AI 3+ sites; N-lines (691, 698, 703, 706 and 711 nm) arise from several types of exchange-coupled pairs of Cr 3+ ions occupying first, second and third nearest and related neighbour AI 3 + sites. It is shown that the absorption bands in the 690-580 nm region of natural pale blue beryl crystals caused by neutron irradiation belong to a complex center, which consists of Cr 3+ ions and radiation defect -F or F + -center. Presence of Fe 2+ ions contributes to the persistence of the complex defect.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
Natural and c-irradiated pink and colorless beryl from Brazil has been investigated by electron paramagnetic resonance (EPR), optical absorption and infrared absorption. Beryl has the chemical formula Be 3 Al 2 Si 6 O 18 and is hexagonal with space group P6/mcc. Electron microprobe analysis of the different samples shows that the beryl samples are rich in Cs (3.30 wt.%) and contain low concentrations of transition-metal ions, in total 0.03wt.0.03 wt.% Fe and 0.03wt.0.05 wt.% Mn. In addition to the transition-metal ions, beryl accommodates many molecules and alkalis in its channels, which lie parallel to the c-axis and which have large diameters with a maximum of 5.1 A A. Infrared absorption measurements in the different samples indicate the presence of type-I and type-II water together with OH À . Other molecules in the channels with not yet associated infrared absorptions are NO 0 3 and CO À 3 which have been observed by EPR. In this work we focus on the EPR identification of the different molecules and discuss their relation to color. Ó
SILVER ATOMS IN THE STRUCTURAL CHANNELS OF BERYL
A silver atom in synthetic beryl is investigated by the EPR and electron spin echo (ESE) spectroscopy. It is established that silver ions were first introduced into the structural channels of beryl by thermodiffusion at 800C. The Ag+ ions are then converted to the Ag0 state by the X-ray irradiation of samples at room temperature. Charge changes in manganese and chromium impurities located at the aluminum positions are observed at the same conditions. Four different Ag0 centers with isotropic hyperfine interactions (HFI) with 107Ag and 109Ag nuclei and hyperfine constants less than those for the free Ag atom are revealed by the EPR method. ESE investigations enable us to confirm the positions of silver atoms that are stable up to 230 C.
American Mineralogist, 2009
Incorporation of water in anhydrous synthetic beryl was studied at 500-700 °C and 50-150 MPa of confining water pressure to measure the diffusion of water molecules along the channels in a cyclosilicate. A series of polarized IR spectra series were taken with E parallel to the channel direction, which is parallel to the c-axis, along a traverse parallel to this axis. Water concentration profiles were determined from absorbance of H 2 O peaks. The IR spectra showed that the dominant diffusing species is type I water molecule, whose H-H vector is parallel to the c-axis (sharp peak at 3700 cm −1). No pressure dependence on water diffusivity can be recognized under these experimental conditions. The Arrhenius relation gives the activation energy of 133 ± 12 kJ/mol, with a pre-exponential factor of 10 −2.6 (cm 2 /s). Diffusion of water is much faster in the beryl channels than volume diffusion in other silicates, but the activation energy and diffusion coefficient values for beryl are similar to the corresponding values previously reported for grain boundary diffusion in quartz aggregates.