Atomic resolution imaging of beryl: an investigation of the nano-channel occupation (original) (raw)
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Mineralogical Magazine, 2008
O 18 ) have been attributed either to the presence of chromophore ions partially replacing Al and/or Be (Cr 3+ , Fe 2+/3+ , Mn 2+ ) or to the occurrence of colour centres related to the presence of multi-atomic groups. However, no full explanation has been proposed for the blue colour in natural beryl gemstones (aquamarine) despite it being well established that bluish-green synthetic aquamarines containing Fe turn blue when heated for 1 h at 400ºC.
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
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.
The single-crystal, polarized-light, FTIR spectrum of stoppaniite, the Fe analogue of beryl
Physics and Chemistry of Minerals, 2007
We report here a single-crystal polarized-light study of stoppaniite, ideally (Fe,Al,Mg) 4 (Be 6 Si 12 O 36 ) (H 2 O) 2 (Na,ᮀ), from Capranica (Viterbo). Polarized-light FTIR spectra were collected on an oriented (hk0) section, doubly polished to 15 m. The spectrum shows two main bands at 3,660 and 3,595 cm ¡1 ; the former is strongly polarized for E rc, while the latter is polarized for E //c. A sharp and very intense band at 1,620 cm ¡1 , plus minor features at 4,000 and 3,228 cm ¡1 are also polarized for E //c. On the basis of literature data and considering the pleochroic behavior of the absorptions, the 3,660 cm ¡1 band is assigned to the 3 stretching mode and the 1,620 cm ¡1 (associated with an overtone 2* 2 at 3,230 cm ¡1 ) band to the 2 bending mode of "type II" water molecules within the structural channels of the studied beryl. The sharp band at 3,595 cm ¡1 is not associated with a corresponding 2 bending mode; thus it is assigned to the stretching vibration of O-H groups in the sample. The minor 4,000 cm ¡1 feature can be assigned to the combination of the O-H bond parallel to c with a low-frequency metal-oxygen mode such as the Na-O stretching mode. The present results suggest that the interpretation of the FTIR spectrum of Na-rich beryl needs to be carefully reconsidered.
Mineralogical Magazine, 2021
Beryl from Xuebaoding, Sichuan Province, western China is known for its unusual tabular habit and W–Sn–Be paragenesis in a greisen-type deposit. The crystals are typically colourless transparent to pale blue, often with screw dislocations of hexagonal symmetry on the (0001) crystal faces. Combining electron microprobe analyses and laser ablation inductively coupled plasma mass spectrometry with single-crystal X-ray diffraction (XRD), correlated with Raman and micro-infrared (IR) spectroscopy and imaging, the crystal chemical characteristics are determined. The contents of Na+ (0.24–0.38 atoms per formula unit (apfu)) and Li+ up to 0.38 apfu are at the high end compared to beryl from other localities worldwide. Li+ substitution for Be2+ on the tetrahedral (T2) site is predominantly charge balanced by Na+ on the smaller channel (C2) site, with Na+ ranging from 91.5% to 99.7% (apfu) of the sum of all other alkali elements. Cs+ and minor Rb+ and K+ primarily charge balance the minor M2+...
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.
ICP, IR, Raman, NMR investigations of beryls from pegmatites of the Sudety Mts
Journal of Molecular Structure, 2005
Detailed ICP, IR, Raman and NMR investigation were performed for more than 50 samples of beryls from pegmatites in the Sudety Mts. MIR spectra were measured at room (293 K), low up to 22 K and high up to 1273 K temperatures. The absorption bands for studied samples of beryl are correlated with chemical composition and structural parameters. The samples represent both alkali-poor (potassium-bearing, sodium-potassium-bearing) and alkali-rich (sodic and sodic-lithian) members of the beryl group. Two types of H 2 O molecules are discerned in all studied beryls. The I-type is not connected with alkali with bands at 3697/3690 cm K1 , 3647/3630/3610 cm K1 (3606 cm K1 in Raman spectra) and 1602/1550 cm K1 dominates over the II-type (hydrated anions of alkali) with bands at 3660 cm K1 , 3592/3590 cm K1 (3597 cm K1 in Raman spectra) and 1637/1630 cm K1 . CO 2 molecules (2360 cm K1 in MIR spectra, 1386 cm K1 , 1240 cm K1 in Raman spectra) and hydroxyl groups in subordinate quantities occur in structural channels of beryls, except for mentioned above. Main bands in the range of 1200-400 cm K1 are diagnostic in discerning of the three types of beryls according to lattice parameter classification. Studied beryls, in the most cases, belong to normal-type. Some samples are octahedral-type, and do not occur tetrahedral beryls in the Sudety Mts. q
Coloration of natural beryl by iron ion implantation
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
Natural colorless crystals of Ural beryl were implanted at room temperature with 40 keV Fe þ ions with fluences in the range of 0.5-1.5 Â 10 17 ion/cm 2 . As-implanted samples show dark-grey tone due to radiation damage of beryl crystal. Subsequent thermal annealing of irradiated crystals in oxygen at 600°C for 30 min results in the color change, to yellowish or yellow-orange tones with golden luster, depending on value of iron fluence. The nature of beryl coloration was studied by optical absorption, M€ o ossbauer and Rutherford backscattering (RBS) spectroscopes. It was established that the thermal treatment of iron-irradiated beryl lead to inward diffusive redistribution of iron ions. An appearance of optical absorption bands connected with charge-transfers O 2À ! Fe 3þ VI and O 2À ! Fe 2þ IV , Fe 3þ IV determine the yellow tone in colored beryls. Most of implanted iron ions are founded in both tetrahedral Fe 2þ IV and octahedral Fe 3þ VI sites where they may substitute beryllium and aluminum host ions by isomorphic way.