|
||||||||
Europium doped crystalline Ba7F12Cl2 phosphors have been prepared at temperatures between 650 and 900 °C using alkali chloride fluxes, yielding both disordered (with the incorporation of small amounts of Na) and ordered crystal modifications. The white emission spectrum excited in the near UV consists roughly of two broad emission bands at ca 450 and 590 nm, as well as weak sharp Eu2+ 4f-4f emission bands around 360 nm. The incorporation of Eu2+ is further studied using EPR spectroscopy on single crystals, and reveals a significant zero field splitting. The emission spectrum can be significantly tuned by varying the excitation wavelength between 300 and 390 nm. Fine tuning may also be achieved by chemical substitutions to form Ba7-xMyF12Cl2-zBrz (M = Na, Ca,Eu). Quantitative measurements of the light produced using commercial near UV LEDs show that the color temperature ranges between 4000 and 9700 K with CIE chromaticity coordinates close to the ideal values of x=y=0.333. The best color rendering index (CRI) found was 0.83, and the highest light to light conversion yield was 171 lumen/W. These results show that the title compound is a very promising candidate for white light generation using near UV LED excitation. |
|
||||||||
In analogy to the synthesis of polycrystalline M2NaIO6 (M = Ca, Sr, Ba) by precipitation in water at 90 °C, the title compound was first prepared as a metastable compound. The stable modification of Pb2NaIO6 was obtained by a heat treatment to 400 °C followed by cooling to room temperature. The crystal structure was refined from powder diffraction data [space group P21/c (14), a = 5.9040(2), b = 5.7526(2), c = 10.1104(3) Ă
, β = 125.341(1)°]. On heating, at ca. 125 °C, a phase transition to a cubic high temperature modification was observed. The crystal structure was refined from XRD data measured at 200 °C [space group Fm3m (225), a = 8.2678(1) Ă
]. Depending on the precipitation temperature between 90 °C and 0 °C, several metastable modifications were obtained, which can be distinguished by significantly different lattice parameters. The XRD pattern of a powder precipitated at room temperature is pseudocubic. The crystal structure was refined at room temperature in P21/c with a = 5.8201(4), b = 5.8473(4), c = 10.0798(5) Ă
, β = 125.074(3)°. This modification behaves almost as a cubic lattice on heating as found from XRD and DSC measurements. |
|
||||||||
The compound Ba5I2O12 was synthesized by heating a precipitate of dissolved Ba(OH)2¡8H2O and H5IO6. Rb2O was added to increase the crystallite size. The crystal structure was determined from conventional laboratory X-ray diffraction data by using a real-space structure solution approach followed by a Rietveld refinement. No constraints on positions were used. The structure analysis gave an orthorhombic symmetry with a = 19.7474(2) Ă
, b = 5.9006(1) Ă
and c = 10.5773(1) Ă
. The final RBragg value in space group Pnma (62) was 1.0â%. The structure can be described by layers of a metal and iodine arrangement forming almost pentagonal holes. Raman measurements were correlated with the two IO6 octahedra. Two further barium periodate patterns were observed and indexed. |
|
||||||||
The crystal structures of the M2NaIO6 series (M = Ca, Sr, Ba), prepared at 650 °C by ceramic methods, were determined from conventional laboratory X-ray powder diffraction data. Synthesis and crystal growth were made by oxidizing Iâ with O2(air) to I7+ followed by crystal growth in the presence of NaF as mineralizator, or by the reaction of the alkali-metal periodate with the alkaline-earth metal hydroxide. All three compounds are insoluble and stable in water. The barium compound crystallizes in the cubic space group Fm3m (no. 225) with lattice parameters of a = 8.3384(1) Ă
, whereas the strontium and calcium compounds crystallize in the monoclinic space group P21/c (no. 14) with a = 5.7600(1) Ă
, b = 5.7759(1) Ă
, c = 9.9742(1) Ă
, β = 125.362(1)° and a = 5.5376(1) Ă
, b = 5.7911(1) Ă
, c = 9.6055(1) Ă
, β = 124.300(1)°, respectively. The crystal structure consists of either symmetric (for Ba) or distorted (for Sr and Ca) perovskite superstructures. Ba2NaIO6 contains the first perfectly octahedral [IO6]5â unit reported. The compounds of the ortho-periodates are stable up to 800 °C. Spectroscopic measurements as well as DFT calculations show a reasonable agreement between calculated and observed IR- and Raman-active vibrations. |
|
||||||||
The crystal chemistry of the barium fluoride chloride system is studied both experimentally and theoretically. Different synthetic approaches yield nanocrystalline materials as well as large single crystals. The crystalline phases identified so far are BaFCl, Ba12F19Cl5 and Ba7F12Cl2 (in two modifications) and compared with analogous compounds. It is demonstrated that the compound Ba2F3Cl reported by Fessenden and Lewin 50 years ago corresponds to Ba7F12Cl2. The phase diagram of the BaCl2 â BaF2 system is reinvestigated for fluoride mole fractions between 0.5 and 1. The peritectic formation of Ba12F19Cl5 is observed. Periodic DFT calculations are performed for all structures in this system, including a hypothetical structure for Ba2F3Cl, based on the experimental structure of Ba2H3Cl. The energy of formation of the different barium fluoride chloride compounds from BaCl2 and BaF2 (normalized for one barium atom per formula unit), as calculated by DFT at 0K, is within only about Âą 15 kJ/mol. Comparison with recent experimental results on calcium and strontium hydride chloride (bromide) compounds, suggest the possibility of a mutual exclusion between the M2X3Y and M7X12Y2 (M = Ca, Sr, Ba, Pb, X = H, F, Y = Cl,Br) structures. The single crystal structure of PbFBr is also reported. |
|
||||||||
The title compound, an achiral flexible molecule containing a 1,2,3-triazole structure as the acceptor subunit, crystallizes as a single enantiomorph in the space group P212121. The material exhibits nonlinear optical properties and is capable of second harmonic generation. Thus, the developed molecular scaffold represents an interesting novel type of NLO chromophore. |
|
||||||||
Barium calcium magnesium fluoride (Ba2(BaxCa1-x)Mg4F14, x=0.19-0.26) has been synthesized at 850 °C from precursors prepared by the solution precipitation method. Single crystals with composition of Ba2.200(2)Ca0.800(2)Mg4F14were obtained after prolonged heating. Lattice parameters from single crystal data are a = 12.4203(8) and c = 7.4365(5) Ă
[tetragonal, space group P42/mnm (No. 136)]. They increase with increasing barium concentration within a given stability window. The structure is built of a network of MgF6Â octahedra forming a pyrochlore related channel system and isolated fluorine ions. Within the channels, heavy alkaline earth ions are located. The wide channel is filled with off-center positioned barium ions. The channel with a narrow cross section hosts both ions, Ca2+and Ba2+. The structure is isotypic with Pb3Nb4O12F2Â but has a different coordination around Ba/Ca and Pb, respectively. Doped with âź1% Eu(II), the compound shows intense blue luminescence under UV activation. |
|
||||||||
The crystal structure of recently reported Ba,F,Cl nanorods is shown to correspond to the structure of Ba7F12Cl2 (see picture), which can be prepared by several growth techniques. |
|
||||||||
The effect on crystal structure and vibrational frequencies of physical pressure in BaFCl and chemical pressure in Ba1âxSrxFCl solid solutions is studied using periodic density-functional theory (DFT) calculations performed within the local-density approximation (LDA) and the generalized gradient approximation (GGA). These results are compared with previously published experimental data for BaFCl in conjunction with new experimental data for Ba1âxSrxFCl and show overall a good agreement with experiment. The GGA method outperforms the LDA method for the description of BaFCl under pressure. However, the two DFT methods perform equally well for the description of the solid solutions, which have been studied within the virtual-crystal approximation. They also give consistent values of the energy of formation of Ba1âxSrxFCl, which can be correlated with the experimentally observed melting points. The comparison of the calculated mode GrĂźneisen parameters shows that, for the investigated systems, the effect of the chemical pressure and that of the physical pressure are not identical. |
|
||||||||
A series of mixed crystals with general formula Ba7-xNayF12Cl2-zBrz in the ordered modification (space group P-6) has been studied by single crystal x-ray diffraction. Depending on synthesis conditions, the disorder in the channels (i.e. occupation of 0 0 z sites) can be changed. The disorder is found to be correlated with the refined Na content, and its effect on Ba-Cl(Br) bond length is discussed. |
|
||||||||
SrMgF4 was prepared by precipitation in aqueous solution. Alkaline earth metal acetates and ammonium fluoride were used as precursors. After drying and annealing the samples at different temperatures and times, single phase SrMgF4 was obtained. By varying the annealing conditions, the mean crystallite size could be adjusted. Furthermore, the thermally treated samples displayed UV-excited intensive broad band luminescence in the visible region. The emissions colour and intensity can be adjusted by the tempering conditions. X-Ray diffraction, TEM-microscopy, fluorescence and IR-spectroscopy were used for analysis. |
|
||||||||
A new barium silico-aluminate phase with the stoichiometry Ba13.35(1) Al30.7 Si5.3 O70 has been found and characterized. The compound crystallizes in the space group P63 /m (No. 176) with a = 15.1683(17) Ă
, c = 8.8708(6) Ă
, V = 1767.5(4) Ă
3 , Z = 1, Rw = 0.026, 32 reďŹned parameters. A 3-dimensional matrix of Al/SiO4 tetrahedra with Ba(II) ions located in channels along the c axis builds up the structure. One of these channels is partially ďŹlled with Ba(II) ions (CN 6+3) in Wyckoff position 2a, leaving âź 1/3 of the positions empty. The second and third type of Ba(II) ions occupy channels orientated along the c axis with CN 4+2+2 and 4+3+1, respectively. The structure shows a rare clustered arrangement of six tetrahedra ďŹlled exclusively by Al(III) and therefore is an exception to Loewensteinâs rule. The other tetrahedral positions show an Al to Si ratio of âź 4 : 1. The Al/SiâO bond lengths in the tetrahedral Al/Si positions drawn vs. site occupation show linear behavior similar to the prediction by Vegardâs rule for solid solutions. After doping with Eu(II) the compound shows bright orange-yellow luminescence with an unusual large shift of the Eu(II) emission band. |
|
||||||||
Mixed single PbFBr1âxIx crystals have been prepared. X-ray powder diffraction structure determinations show that all samples crystallize with the matlockite structure. However, the single crystal structure of PbFBr0.5I0.5 involves not only fractional occupation of one site corresponding to the stoichiometry, but also split positions of the Pb2+ ion. Raman spectra reveal the presence of new additional bands with respect to PbFBr and PbFI. DFT calculations of lattice vibrations for PbFI show good agreement with experimental spectra. The calculated phonon dispersion curve suggests that for the mixed crystals the centre of inversion is conserved locally. These combined results suggest the presence of domains with ordered FâPbâBrâBrâPbâF and FâPbâIâIâPbâF layers in the mixed crystals. Calculations on PbFBr0.5I0.5 show that this suggested structure is more stable than the structure consisting of the FâPbâBrâIâPbâF arrangement. |
|
||||||||
The crystal structure of the disordered modification of Ba7F12Cl2 has been carefully re-examined on several new crystals prepared under different conditions of synthesis. All single crystal structure refinements reveal a residual electron density of ~3 e-/Ă
3 in the 0,0,0 position which is explained by the introduction of a small amount of sodium ions in the crystal. The title compound transforms from a disordered to an ordered modification at ~800 °C. New structural data show a change in space group from P63/m to P6. During this process, a slight chemical change and the formation of nano-channels in the crystals is observed by electron microscopy. These changes were further studied by electron microprobe analysis, by spectroscopic methods and thermal analysis. |
|
||||||||
Mixed matlokite hosts of composition BaFBrxI1âx(0â¤xâ¤1) (pure and doped with Sm2+, Eu2+) were studied with x-ray crystallography, luminescence, Raman, and electron paramagnetic resonance (EPR) spectroscopy. Results are presented for BaFBr0.5I0.5 which demonstrate that a ferrielectric domain structure is formed due to the fact that the heavy halogen ions form separate sublattices with randomly distributed domain walls. The space group of a domain is P4  mm (No. 99). The EPR data from Eu2+ allowed to determine the volume fraction of domains. |
|
|||||||||||
|
|
||||||||
Temperature-dependent emission spectra of Sm2+-doped SrMgF4 have been obtained in the temperature range from 50 to 300Â K. At 50Â K, six bands are observed for the very strong 5D0â7F0 transition, in agreement with the reported sixfold crystal superstructure. The overall splitting of more than 70Â cmâ1 highlights the important structural differences of the six Sr sites. Upon heating progressively to room temperature, the spectra change progressively with a more pronounced change between 270 and 300Â K. These observations suggest the possibility of a complex structural behavior for SrMgF4 which will require new experiments. |
|
||||||||
Ba6Mg11F34, a new compound of the pseudobinary BaF2âMgF2 system, has been synthesized by solid state techniques from stoichiometric amounts of BaF2 and MgF2 and its crystal structure determined by single crystal X-ray diffraction (space group P1 , a=7.5084(6), b=9.9192(8), c=10.0354(8)Â Ă
, Îą=81.563(2), β=72.402(2), Îł=71.198(1)°, 3899 structure factors, 233 parameters, R(F2>2Ď(F2))=0.018, wR(F2 all) = 0.046). It is isotypic with the copper(II) analogue, Ba6Cu11F34. The main features of the structure are a network of [MgF6] octahedra and three different [BaFx] polyhedra with x=12, 11+1 and 13. Ba6Mg11âxFexF34 and Ba6Mg11âxMnxF34 solid solutions were prepared and their composition determined by single crystal structure analyses. The luminescence properties of Ba6Mg11F34 doped with Eu2+ were studied using fluorescence spectroscopy. The observed luminescence was pale blue with a maximum at 465 nm. |
|
||||||||
Crystals of ordered Ba6EuF12Cl2 were found to form during high temperature flux growth. The structure was refined in the hexagonal space group P 6 to RF(RFW) = 0.024(0.024) for 326 reflections and 46 parameters. Lattice parameters are a = b = 1059.27(8) pm and c = 416.36(2) pm; Z = 1. The structure is isotypic to Ba7F12Cl2. No solid solution of Ba/Eu was observed, the Eu2+ ions are located in the channels formed by 3 + 6 fluorine ions, occupying only one of the three metal sites of the Ba7F12Cl2 structure. |
|
||||||||
We recently discovered a new compound with composition Ba7F12Cl2. It was possible to show that the variation of the synthesis conditions makes it possible to obtain a disordered and an ordered modification with different lattice parameters and space groups (P63/m [176] and P6  [174]). For Pb7F12Cl2 an ordered modification is reported in the literature. In this paper we present the synthesis and structural characterization from X-ray diffraction data of the disordered modification of Pb7F12Cl2. Single crystals were grown from a flux and the structure was refined in the hexagonal space group P63/m to R(Rw)=0.043(0.038) for 284 reflections and 26 parameters. Lattice parameters are a=b=1021.90(8) pm and c=361.93(6) pm with Z=1. Propeller-type arrangements with chlorine as axis and fluorines as blades are observed. The ordered modification of Pb7F12Cl2 was prepared by a new hydrothermal synthesis. Differences between both modifications are found in the lattice constants and atomic occupation parameters for the atom type Pb2 and the connected fluorine ions. |
|
||||||||
Polylactic acid (PLA) is a biocompatible and biodegradable material with wide utility for many applications, including the design of controlled-release systems for pharmaceutical agents. The factors determining the degradation kinetics of these systems include the composition and the molecular mass of the polymer, the morphology and the structure of the device, and the influence of thermal processes. The processing of the polymer determines the structure and design of the device, and influences to a high degree its morphology, namely its microporous structure, polymeric chain orientation and crystallinity. In this work, we aimed to compare the influence of two different implant manufacturing techniques, extrusion and injection-molding, on the in vitro degradation of the polymeric matrix. Both kinds of implants were loaded with a somatostatin analogue. Decrease in molecular weight, and polydispersity evolution during an accelerated in vitro degradation test were studied by size exclusion chromatography. Morphological changes in the polymeric matrix during degradation were followed after defined time intervals by means of scanning electron microscopy. Crystallinity studies were performed by differential scanning calorimetry and by X-ray analysis. Peptide stability in the polymeric matrix after both manufacturing methods was evaluated. Peptide release profiles, obtained in vitro during a week dissolution test, from both implant samples, were studied. It was shown that both molecular weight and polydispersity decreased after extrusion or injection-molding. This decrease was more pronounced with the latter technique. Crystallinity studies demonstrated that the crystalline network was not destroyed after both manufacturing methods. Peptide release profiles obtained in vitro were in good accordance with scanning electron microscopy. It was found that both manufacturing techniques had to be considered, although the extruded implants degraded more rapidly in vitro than the injection-molded ones. |
|
||||||||
Barium in BaMgF[4] and in Ba[6]Mg[7]F[26] can be partially replaced by Sr or Eu. The single crystal structural analysis of the title compounds (a = 409.06 pm, b = 1452.7 pm, c = 579.02 pm, space group Cmc2[1] for Ba[0.78(3)]Eu[0.22(3)]MgF[4] [Z = 2, R[w] = 0.023 for 998 reflections] and a = 583.47 pm, b = 1209.09 pm and c = 1506.56 pm, space group Immm for Ba[5.20(6)]Eu[0.80(6)]Mg[7]F[26]) MgF[4] [Z = 2, R[w] = 0.019 for 2694 reflections] confirms the substitution of barium by europium. A split refinement of the substituted barium site in both crystals reveals a trend of europium to get closer to the nearest fluoride neighbors by simultaneously reducing the coordination sphere. |
|
||||||||
Crystals of composition Ba7F12Cl2 were obtained by a reaction at room temperature between Ba2+/Cl-/F- in a gel of agar-agar/water. The hexagonal crystals have space group P6, a=1064.69(8), c=417.89(5)pm, V=410.24(8) 106 pm3 and Z=1. The anions form a propeller type network located in tunnels parallel to the chex axis; the chloride ions are located at the center on the propeller axes. The Ba2+ ions are coordinated by a (distorted) tricapped trigonal environment of fluoride and chloride anions. Disorder is present for one particular Ba2+ site. The average structure is isotypic with the structure of Pb7F12Cl2. |
|
|||||||||||
|
|
||||||||
Li2S, cubic, Fiiβm (No. 225), a = 5.7158(1) A, V= 186.7 A3, Z = 4, REi(F) = 0.009, Rv.(F) = 0.009, T= 293 K. |
|
||||||||
Single crystals of the new host Ba12F19Cl5Â doped with Eu2+Â were grown and studied by electron paramagnetic resonance (EPR) and luminescence emission spectroscopy. Three different Eu2+Â sites were observed. Two of them had orthorhombic point symmetry while the last one was monoclinic. Physico-chemical and symmetry arguments allowed us to establish correspondence between the different Eu2+centres and the host cation lattice sites. All three centres presented in their ground state important crystal field splitting. The 80 K luminescence emission spectrum consisted of one broad unsymmetrical f-d band peaking at 22 700 cm-1. No 4f-4f transitions of the Eu2+Â ion were observed between room temperature and 80 K. |
|
||||||||
We have studied the solid-liquid equilibrium of the system Sr1âyBayFCl1âxBrx using DTA and X-ray diffraction techniques. The entire composition range in this system yields solid solutions which crystallize in the PbFCl (Matlockite) structure type. The melting points of the entire composition range have been parametrized (within 5°C rms error) using a biquadratic fit of the available data obtained by experiment and from the literature. |
|
||||||||||||
|
|
||||||||
In orthorhombic Ba6Mg7F26, the Ba2+ ion can be partially replaced by Sr2+ to form a mixed, disordered compound. This new compound has a refined composition of Ba5.24 (4)Sr0.76 (4)Mg7F26. The volume decreases after the partial substitution from 1074.64 (10) to 1064.31 (11) Ă
3. The structure has two barium sites, Ba1 on Wyckoff site 8(l) with Cs symmetry and a coordination number of 12 + 1, and Ba2 on site 4(j) with C2v symmetry and a coordination number of 12; only the Ba2+ on site 4(j) is partially replaced by Sr2+. The distorted octahedral fluoride environment around magnesium shows a tendency to become more irregular in the Sr-substituted compound. |
|
||||||||
The crystal structures of cubic and tetragonal NiCr2O4 and of tetragonal CuCr2O4 have been refined and their cell parameters have been measured, using single-crystal and powder X-ray diffraction. It has been observed that the differences in the JahnTeller distortions in both compounds are reflected in their M2+ O tetrahedral environments and in their cell parameters. A calculation of the atomic shifts during the tetragonalcubic phase transition showed that the average shifts for the oxygen atoms are 0.10(1) and 0.04(1) Ĺ for the nickel and chromium atoms, respectively. Crystals of both compounds jump when they go through the phase transition. This behaviour is especially spectacular for NiCr2O4 since the phase transition takes place at 320 K, this temperature being reached when the crystals are illuminated. A comparison with organic jumping crystals is presented, and characteristics of the chromite crystals are discussed. |
|
|
||||||||
The present investigation is concerned with the possible effects of material-related properties (molecular mass, glass transition and melting temperatures, crystallinity, tacticity) and particle-related properties (shape, size, specific surface area) on the compression characteristics of the chosen model polymer powder: poly(vinyl chloride) (PVC). Four grades were selected known in literature for providing compacts of varied mechanical strength. The compression characteristics were determined using an instrumented single-punch tableting machine. The differences in tableting characteristics could not be ascribed to any of the material-related properties, but a direct relationship was observed between the compact strength and the specific surface area of the particles, as measured by nitrogen adsorption. The compact hardness was thus only dependent on the inter- and the intraparticulate contact area, which in turn is dictated by the very peculiar morphology of the grains of the PVC powders, whether prepared by emulsion or suspension polymerization. |
|
||||||||
Single crystal X-ray diffraction analysis was performed on crystals with composition Ba1 â δSrδMgF4 (δ ⤠0.55). The complete structure was analyzed for single domain crystals with nominal (refined) values of δ = 0.25 (0.27(2)) and 0.5 (0.55(2)). Interatomic distances vary in a characteristic manner, when smaller strontium ions replace the barium ions. Optical studies of Sm(II) doped samples show significant inhomogeneous line broadening and confirm the disorder On the Ba Site. |
|
||||||||
We study the ionic conductivity versus temperature and frequency of large Na2S single crystals by using a calibrated impedance apparatus. The experimental setup used for the ionic conductivity measurements up to 1350 K and its calibration are described. The apparatus allows to measure complex impedances between 0.1 Ί and 10 GΊ. The high temperature conductivity data were analyzed in terms of the conventional Frenkel defect model. We assume that cation vacancies and cation interstitials are the dominant intrinsic defects. The energy of motion was found to be 0.61 Âą 0.05 eV for a cation vacancy. The energy of formation of a Frenkel defect pair is 2.51 Âą 0.05 eV. Results are given that show clear evidence of a superionic behaviour close to the melting point, similar to the one found in alkaline earth fluorides and several halides. Furthermore, X-ray diffraction experiments on a high optical quality single crystal were performed. The cell parameter and the population parameter of Na+ were accurately determined (6.5373 Ă
and 0.988, respectively). |
|
||||||||
A new member belonging to the binary phase diagram of BaF2 and BaCl2 was synthesized. The single domain crystals of Ba12F19Cl5 can be prepared from a nonstoichiometric flux with molar ratio of 1 : 1 between BaFCl and BaF2. The compound crystallizes at room temperature in the non-centrosymmetric hexagonal space group P62m with a = b = 1408.48(14) and c = 427.33(5) pm. Three different barium environements with coordination number of nine are found. The barium fluorine distances vary between 250.59(6) - a short distance compared to other Ba â F distances - and 302.7(1) pm and barium chlorine distances between 331.55(3) and 336.19(15) pm. This compound is further characterized using Raman spectroscopy. |
|
||||||||
In the structure Ba12F19Cl5 [hexagonal space group P62m] the two chlorides on the sites Cl(1) and Cl(2) can partially be replaced by bromide ions. Single crystals of the type Ba12F19Clδ Br5-δ  with a chloride to bromide ratio up to 2 : 3 could be obtained by cooling a flux of 75 mol% BaF2 and 25 mol% BaX2 with X = Cl, Br. The crystal quality decreases with increasing bromide concentration. Structural parameters of five selected single crystals with different chloride/bromide ratio were studied by single crystal X-ray diffraction methods. The refined total Cl-/Br- population ratio in the crystals is close to the one of the flux. The lattice parameters and interatomic distances change in various ways, when the smaller chloride ion is replaced by the bigger bromide ion. The refinements show a statistical disorder on the halide sites with preferential bromide substitution on site Cl(1). |
|
||||||||
The compound Sr4OCl6 was synthesized and its crystal structure was determined by using a ferroelectrically single domain crystal. The structure is similar to those of other M4OCl6 compounds where M=Ca,Yb,Eu,Sm and Ba. Interatomic distances are compared with these compounds. The Raman spectra of Sr4OCl6 and Ba4OCl6 are compared. |
|
||||||||
Single crystals X-ray diffraction was performed on five crystals with nominal compositions Sr1/2Sm1/2FCl, Sr1/2Ca1/2FCl, Sr2/3Ba1/3FCl1/3Br2/3, Sr1/2Sm1/2FCl1/2Br1/2 and Sr0.6Sm0.1Ca 0.3FCl. Population refinements confirm the presence of correlations between lattice constants and composition. A new correlation between the heavy halogen z value and the unit cell volume is found. Luminescence spectra of bivalent samarium in these crystals contribute to the structural characterization of these compounds. |
|
||||||||
We present the results of a crystallographic and optical study realized on the system SryBa1-yFClxBr1-x where x and y vary from zero to one. All mixed crystals studied were of tetragonal symmetry with the parent PbFCl structure. Complete structure determinations were performed for two single crystals with y=0.3 and x=1 respectively 0.7 (nominal composition). This system forms complete solid solutions, in contrast to previously published results. |
|
||||||||
We report on crystal growth and about physico-chemical studies on SryBa1âyFClxBr1âx (y = 0, 0.5, and 1) compounds doped with Sm. Persistent spectral hole burning at 300 K is further reported on Sr0.5Ba0.5FCl0.5Br0.5:Sm single crystals. |