A series of rare earth silicates RE3+2M3+[SiO4]2 (OH)

A series of isotypic silicates of composition RE₂M[SiO₄]₂ (OH) with RE = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and M = Al³⁺, Fe³⁺ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La₂Al[SiO₄]₂ (OH) (La₂Fe[SiO₄]₂ (OH)) $\text{a}{}_{\mathrm{o}}\text{= 7.401 (7.346)}\text{A}\text{?}$, $\text{b}{}_{\mathrm{o}}\text{= 5.702 (5.862)}\text{A}\text{?}$, $\text{c}{}_{\mathrm{o}}\text{= 17.072 (97.196)}\text{A}\text{?}$, gb = 112.4 (112.5°), $\text{P}\text{2}{}_1\text{c}$, Z=4.     

Interactions magnetiques hyperfines et quadrupolaires combinees pour les ions d'impuretes 119Sn2+ dans Cr2O3

Hyperfine magnetic interactions have been observed for the first time for Sn²⁺ ions introduced as doping agents in a magnetically ordered oxide (¹¹⁹Sn: Cr₂O₃). Mössbauer resonance at low temperature shows for ¹¹⁹Sn²⁺ the simultaneous presence of hyperfine magnetic and quadrupole interactions, which have the same order of magnitude at 77 K. From the spectra, the following parameters have been determined: tranfered hyperfine magnetic field: H_Sn²⁺ (77 K = 38 ± 1kOe, sign and value of the quadrupole interaction constant: eV_zzQ = + 3,6 ± 0,3 mm/s, asymmetry parameter: η = 0,15 ± 0,05, polar (θ) and azimutal (?) angles: $\text{θ ? ? ? 90°}$, and chemical shift: $\text{δ}\text{BaSnO}{}_3\text{= + 2,89 ± 0,02}\text{mm}\text{/}\text{s}$. The investigation shows that Sn²⁺ is localized at the surface of the Cr₂O₃ grains.     

Etude par rpe de Ni2+ dans RbMgF3 de structure 6H

The crystal structure of 6H-RbMgF₃ has been more precisely determined by using the crystal data of isostructural RbNiF₃. It crystallizes in the hexagonal P6₃/mmc space group with the parameters: $\text{a}\text{= 5.833}\text{A}\text{?}$ and $\text{c}\text{= 14.193}\text{A}\text{?}$.Both magnesium positions can be occupied by Ni²⁺ and detected by ESR. Analysis of the spectra reveals one site (octahedra sharing one face) corresponding to an important zero field splitting (D = 2,37 cm^?1) and another one of higher symmetry corresponding to the corner-sharing octahedra.     

Luminescence properties of Dy-doped Li2SrSiO4 for NUV-excited white LEDs

A series of single-phase full color phosphors, Dy³⁺-doped Li₂SrSiO₄ was synthesized by a solid-state reaction method. The phase of the as-prepared powders was measured by X-ray diffraction pattern (XRD) and the chemical composition was characterized using energy dispersive spectroscopy (EDS). The luminescent properties of Li₂SrSiO₄:Dy³⁺ were systematically investigated by concentration quenching, decay behavior and thermal stability measurements. The results suggested that the emission intensity of the Li₂SrSiO₄:Dy³⁺ was much stronger than that of Li₂SrSiO₄:Eu²⁺. It was worth to mention that Li₂SrSiO₄:Dy³⁺ phosphor possessed excellent thermal stability for use in light-emitting diodes (LEDs) and the emission intensity measured at 300 °C was only decreased 8% comparing with that measured at room temperature. Furthermore, the Commission International del’Eclairage (CIE) chromaticity coordinates of Li₂SrSiO₄:Dy³⁺ moved toward the ideal white light coordinates (0.33, 0.33). All results demonstrated that Li₂SrSiO₄:Dy³⁺ might be a potential phosphor for NUV-based white light-emitting diodes.     

Phase investigations in the system PbSIn2S3 and the crystal structures of PbIn2S4 and Pb6In10S21

The system PbS-In₂S₃ was examined by differential thermal analysis (DTA), chemical vapour transport (CVT), and X-ray diffraction. Five new phases of compositions closely related to the 1:1 ratio were found and prepared as needle-shaped single-crystals; their crystal data are reported. The structures of PbIn₂S₄ (orthorhombic, Pnma, a=11.688(1), b=3.8528(1), $\text{c}\text{=13.763(1)}\text{A}\text{?}$, Z=4) and Pb₆In₁₀S₂₁ (monoclinic, C2/m, a=27.629(3), b=3.8630(5), $\text{c}\text{=15.705(2)}\text{A}\text{?}$, β=95.9°, Z=2 were solved from 808 resp. 3554 independent reflexions and refined to R=0.116 resp. 0.068. In both structures the In-S coordination polyhedra are distorted octahedra, the Pb-S polyhedra are distorted bicapped trigonal prisms.     

Systeme Ga2S3PbS diagramme de phase,etude cristallographique

Four intermediate phases are present ; PbGa₂S₄,orthorombic EuGa₂S₄-type (a = 20,44 ; b = 20,64 ; $\text{c}\text{= 12,09}\text{A}\text{?}$) ; Pb₂Ga₂S₅, orthorombic space group Pbca (a = 12,38 ; b = 11,90 ; $\text{c}\text{= 11,03}\text{A}\text{?}$) ; and two Ga₂S₃-rich solid solutions, one of the wurtzite type at temperatures above 1000°C, one of the distorded blende type below about 970°C. PbGa₂S₄ has a peritectic decomposition at 930°C, and Pb₂Ga₂S₅ at 900 ± 5°C. The eutectic is at 730°C for about n = 0,80 ($\text{n}\text{=}\text{Pb}\text{Pb+Ga}$ atomic). A glassy region is obtained by quenching the liquid phase and its extent depends on the quenching temperature (at 1000°C, between n = 0,25 and n = 0,50).     

Studies on the luminescence properties of manganese activated strontium borate SrB6O10

The preparation and luminescence properties of manganese activated strontium borate have been studied. Divalent manganese emits green light at 512 nm in the SrB₆O₁₀ matrix. The emission is weak when excited with UV-radiation but can be improved with sensitizers, $\text{viz.}$ Pb²⁺ and Sn²⁺, having emission in the UV (312 nm) and blue regions (430 nm), respectively. Divalent lead proved to be a better sensitizer than tin and greatest emission brightness was obtained with a Mn²⁺ concentration of 4 % and Pb²⁺ concentration of about 15 %. Complete energy transfer from sensitizer to activator was not obtained with either Pb²⁺ or Sn²⁺.The emission wavelength of (Sr_0.8Mn_0.04Pb_0.16)B₆O₁₀ at 512 nm is somewhat too short for a low-pressure fluorescence lamp containing three phosphors. The wavelength can be slightly lengthened by the addition of Ba, Ca or Cd, but there is then a dramatic decrease in the emission intensity of manganese.     

Preparation and structural characterization of the lead oxide iodide Pb3O2I2

Single crystals of orthorhombic Pb₃O₂I₂ could be prepared by annealing a mixture of 2PbO + PbI₂ at 400 °C. Cell parameters are a = 17.862(3), b = 5.954(1), and $\text{c}\text{= 7.487(2)}\text{A}\text{?}$; space group is Pnma. The structure was determined from 1121 independent reflections and refined to R = 3.16%. It is built up by edge-shared Pb₄O tetrahedra, forming Pb₆O₄ double chains parallel to [010], which are connected by iodine. Three anion coordinations of lead can be distinguished: Pb(1) forms a bicapped triangular prism with 4 oxygen and 4 iodine atoms (4+4), Pb(3) a monocapped prism (2+5), whereas Pb(2) is octahedrally (2+4) surrounded; all coordination polyhedra are distorted. Structural relationships to Pb₃O₂Cl₂ exist.     

The sodium ytterbium orthophosphate Na3(1+x)Yb(2-x)(PO4)3

A new sodium ytterbium orthophosphate with general formula Na_3(1+x)Yb_(2-x)(PO₄)₃ (0.07 ? x ? 0.50) has been prepared and characterized. Its crystal structure has been determined from a single crystal for x = 0.50. The space group is R3?c, the lattice constants are : $\text{a}\text{= 9.12(1)}\text{A}\text{?}$, $\text{c}\text{= 21.81(6)}\text{A}\text{?}$. The structure of Na_4.50Yb_1.50(PO₄)₃ is related to that of NaZr₂(PO₄)₃. The PO₄ tetrahedra and the (Yb,Na)O₆ octahedra form a three-dimensional skeleton in which the remaining sodium atoms are inserted. This structural type is also found for the phases Na_4.50Ln_1.50(PO₄)₃ (Ln = Tm, Lu) and Na_4.50Ln_1.50(AsO₄)₃ (Ln = Er, Tm, Yb, Lu).     

Temperature dependence of critical stress and phase diagram of ferroelastic Pb3 (PO4)2 Pb3 (VO4)2

The temperature dependence of the critical stress in ferroelastic Pb₃ (PO₄)₂ reveals a Curie-Weiß law ($\text{ß =}\text{1}\text{2}$) up to 145°C. Between 160°C and the transition point at 180°C a crossover to a $\text{ß =}\text{1}\text{3}$ regime was found. For mixed crystals Pb₃ (PO₄)₂ ? Pb₃ (VO₄)₂ a phase diagram is suggested from optical, dielectric and Raman spectroscopical experiments.     

Une nouvelle structure ordonnee derivee de la fluorine : Pb3ZrF10

Pb₃ZrF₁₀ crystallizes with orthorhombic symmetry, space group : Cmcm and unit-cell parameters : $\text{a}\text{= 10,713(3)}\text{A}\text{?}$, $\text{b}\text{= 12,817(4)}\text{A}\text{?}$, $\text{c}\text{= 5,909(2)}\text{A}\text{?}$ (Z = 4). Its structure has been solved and refined to a conventional R = 0,041 for 350 independent reflexions. It can be described as an ordered intergrowth of (Pb₂F₄)_n fluorite like monodimensional units and (Pb₄Zr₂F₁₆)_n columnar clusters built of two isolated square antiprisms sharing faces with four [PbF₁₁] complex polyhedra.A structural mechanism based on the transformation of edgesharing fluorite cubes to isolated square antiprisms is proposed to explain the change from fluorite to the anion-excess fluorite like Pb₃ZrF₁₀ structure.Analogies with homologous structures are discussed.     

Une nouvelle structure ordonnee derivee de la fluorine : Pb3ZrF10

Pb₃ZrF₁₀ crystallizes with orthorhombic symmetry, space group : Cmcm and unit-cell parameters : $\text{a}\text{= 10,713(3)}\text{A}\text{?}$, $\text{b}\text{= 12,817(4)}\text{A}\text{?}$, $\text{c}\text{= 5,909(2)}\text{A}\text{?}$ (Z = 4). Its structure has been solved and refined to a conventional R = 0,041 for 350 independent reflexions. It can be described as an ordered intergrowth of (Pb₂F₄)_n fluorite like monodimensional units and (Pb₄Zr₂F₁₆)_n columnar clusters built of two isolated square antiprisms sharing faces with four [PbF₁₁] complex polyhedra.A structural mechanism based on the transformation of edgesharing fluorite cubes to isolated square antiprisms is proposed to explain the change from fluorite to the anion-excess fluorite like Pb₃ZrF₁₀ structure.Analogies with homologous structures are discussed.     

Etude des phases ferroelastiques de Pb3V2O8 : Determination de la maille cristalline de la phase α ferroelectrique basse temperature

The cell parameters of the ferroelastic and ferroelectric phase of Pb₃V₂O₈ (T < 262 K) have been determined by very accurate X-ray powder diffractometry ; at 77 K, $\text{a}\text{= 7.460 (1)}\text{A}\text{?}$, $\text{b}\text{= 6.191 (1)}\text{A}\text{?}$, $\text{c}\text{= 9.348 (1)}\text{A}\text{?}$ and $\text{β = 116.63 (1)}\text{A}\text{?}$. This monoclinic cell is characterized by Z = 2 and the space group is A2. Thermal expansion tensors have been measured versus temperature for the three phases α (T < 262K), β (262K < T < 360 K) and γ (T > 360 K). The intermediate phase β is characterized by an important thermal expansion anisotropy and its molecular volume is higher than that of the two other phases α and γ.     

Interactions of Cr2+ with the F− ligands in CdF2:Cr2+

Superhyperfine structure s.h.f.s. resulting from the Cr²⁺ - F^? interaction was studied in Cr²⁺ doped CdF₂ crystals. The s.h.f.s. observed can be described with by the following spin-Hamiltonian

$\text{H}\text{=}\text{g}{}_{\mathrm{eff}}\text{β}\text{HS}{}_{\mathrm{z}}\text{+ST}{}_{\mathrm{i}}\text{I+ST}{}_{\mathrm{j}}\text{I}$

The constants calculated are $\text{T}{}_{\mathrm{i\perp }}\text{≈}\text{T}{}_{\mathrm{i}}\text{= 50}\text{MHz}$$\text{T}{}_{\mathrm{j\perp }}\text{≈}\text{T}{}_{\mathrm{j}}\text{= 5}\text{MHz}$. The measurements were made with an ESR spectrometer at X band at 4.2 OK.     

Phase analysis studies on the system PbOPbF2Nb2O5NbO2F

Samples in the system PbOPbF₂Nb₂O₅NbO₂F prepared at 875 K and 1025 K were studied by X-ray single crystal and powder diffraction as well as electron diffraction methods. Six new compounds were characterized as Pb_0.74Nb_10.62(O,F)₃₀ (orth.), Pb_1.36Nb_10.91(O,F)₃₀ (tetr.), Pb_0.27Nb(O,F.)_3.17 (hex.), Pb₂Nb₃O₇F₅ (tetr.), Pb_0.75NbO₃F_0.5 (tetr.) and Pb_1?$\text{x}$Nb_$\text{x}$(O,F)_2+$\text{y}$ (cub.)     

LuMnGe2, un nouveau type structural apparente a ceux de TiMn(Fe)Si2, ZrMnSi2 et ZrFeSi2; ScMnGe2, un nouvel isotype de TiMn(Fe)Si2

LuMnGe₂ has been studied by single - crystal X-ray diffraction analysis. The structure is of a new type with space group Cmmm and Z = 12: a = 5.466(2), b = 18.519(7), $\text{c}\text{= 8.173(3)}\text{A}\text{?}$, D_x = 9.03 Mg m^?3, μ(AgKα) = 31 mm^?1, F(000) = 1919, R = 0.030 for 593 independant reflexions (R_w = 0.034). The LuMnGe₂ structure type had been predicted and completes a large structural family TT′Si(Ge)₂ where T = Nb, Ti, Zr, Hf, Sc, Lu and T′ = Cr, Mn, Re, Fe, Co, where ScMnGe₂ is another new member, isostructural with TiMn(Fe)Si₂     

An ESR study of the heterogeneous system Cr2O3V2O5

An ESR study of the ‘products’ of the high temperature solid state reaction xCr₂O₃+yV₂O₅ ($\text{0.05≦(}\text{x}\text{y}\text{)≦2.0}$), aided by powder X-ray diffraction and IR spectra, has revealed (i) ‘unfamiliar’ paramagnetic intermediates Cr⁴⁺ and Cr⁵⁺, (ii) provided some clues to the oxidation of Cr³⁺ to Cr⁶⁺, and (iii) demonstrated a variety of exchange interactions involving V⁴⁺ and Cr³⁺.     

Splitting and broadening of the emission bands of Y2O3:Eu3+,Nd3+ and its dependence on Nd3+ concentration and annealing temperature

Although Eu³⁺ ion-doped Y₂O₃ has been extensively used as red phosphors, their color rendering needs to be improved for high-quality illumination and displaying. Here, we show that the emission spectra of Y₂O₃:Eu³⁺ red phosphors can be broadened by the doping of Nd³⁺ ion so that the color rendering capability of Y₂O₃:Eu³⁺ was remarkably enhanced. Y₂O₃:Eu³⁺ and Y₂O₃:Eu³⁺,Nd³⁺ colloidal spheres were synthesized by wet chemical procedure and high-temperature treatment. The fluorescence measurement under the 254 and 380 nm ultraviolet excitation indicates that the 612 nm red emission peak of Eu³⁺ can be splitted into two ones by the doping of Nd³⁺ ion, of which the full width at half maximum (FWHM) is broadened from 4.2 nm to 9.6 nm. By varying the concentration of Nd³⁺ ion, it was determined that the optimal doping concentration of Nd³⁺ ion is of 3 mol% for realizing the strongest emission intensity. The further increase of Nd³⁺ ion exceeding 3 mol% would lead to a concentration quenching phenomenon. The analysis based on XRD spectra and the simplified energy diagram suggested that the doped Nd³⁺ ion not only monitored the growth dynamics, but also took an efficient energy transfer and a cross relaxation process to generate intense emission from Eu³⁺ ion in both of C₂ and S₆ sites, instead of preferable one type of Eu³⁺ site (C₂ or S₆) in the Nd³⁺ undoped sample.     

Crystal chemistry of (Cd,Me)3(PO4)2 solid solutions

A number of solid solutions of $\text{Me}$₃(PO₄)₂ in Cd₃(PO₄)₂ have been prepared and equilibrated at 1070 K ($\text{Me}\text{=}\text{Mg, Mn, Fe, Co, Ni, Cu, Zn, or Ca}$). The respective ($\text{Cd}{}_{\mathrm{<mtext>1?</mtext><mtext>z</mtext>}}\text{Me}{}_{\mathrm{<mtext>z</mtext>}}\text{)}{}_3\text{(}\text{PO}{}_4\text{)}{}_2$ phases are either isotypic with β′-Cd₃(PO₄)₂ or with the mineral graftonite, both with five- and six- (or even seven)-coordinated cations. The monoclinic unit cell dimensions have been accurately determined from Guinier-Hägg photographs, and complete X-ray powder diffraction data are given for β′-Cd₃(PO₄)₂. The cell volumes are strongly correlated to the size and amount of incorporated $\text{Me}$²⁺ cation. The homogeneity regions and structures of the (Cd,$\text{Me}$)₃(PO₄)₂ phases, though, seem rather to be controlled by the $\text{Cd}{}^{\mathrm{2+}}\text{Me}{}^{\mathrm{2+}}$ cation ordering.     

Existence de la structure triramsdellite : Li3FeSb2O8

An ordered ramsdellite Li₃FeSb₂O₈, called triramsdellite, was synthesized for the first time. This phase crystallizes in the orthorhombic system, with the possible space groups Pmcn and P2₁ cn and with the parameters $\text{a}\text{= 9.017(4)}\text{A}\text{?}$, $\text{b}\text{= 5.013(2)}\text{A}\text{?}$ and $\text{c}\text{= 9.841(4)}\text{A}\text{?}$. The X-ray powder diffraction study shows that a 1–2 type order appears between the cations belonging to the two sorts of octahedral sites A and B; these sites are preferentially occupied by lithium and antimony respectively according to the formulation |Li₃|_tet|Li_1.5Fe_0.5|^A_oct|FeSb₃|^B_octO₁₂. This structure, which can be described as built up from A₂B₄O₁₂ octahedral units, is compared to the LiSbO₃ and trirutile structures.