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The crucible weighing method has been successfully employed to reduce diameter fluctuations of oxide crystals pulled by the CZ technique. All the growth process, including the diameter of the growing crystal, is computer-controlled. A new algorithm for Automatic Diameter Control (ADC) is developed, and a software program written in Labview-6.1(NI) is described in detail.

International audience; Single crystals of Yb doped Li6Y(BO3)3 were obtained by Czochralski method. The first laser tests were encouraging. Different parameters have been investigated to improve cw-laser performances. Thermal properties but also ytterbium content, crystal thickness and pump polarisation are reported. The best crystal configuration was determined and led to high power cw-laser tests equal to 2 W output power.

A new iron titanyl phosphate Fe0.50Ti2(PO4)3 was synthesized by both solid-state reaction and Cu2+–Fe2+ ion exchange method. The material was then characterized by X-ray diffraction, Mossbauer, magnetic susceptibility measurements and optical absorption. The crystal structure of the compound was refined, using X-ray powder diffraction data, by the Rietveld profile method; it crystallizes in the rhombohedral system, space group R 3 ¯ , with a=8.511(1) A and c=20.985(3) A, V=1316.45(3) A3 and Z=6. The structure, which is compared to that of Mn0.50Ti2(PO4)3 is built up from [TiO6] octahedra and [PO4] tetrahedra which are linked by corner sharing along the c-axis. Fe2+ cations are located in half of the antiprism MI sites and are orderly distributed with vacancies within the two possible positions of the MI sites of R 3 ¯ . These results were supported by the Mossbauer studies that showed the presence of one Fe2+ site in the high spin state (t2g4eg2). The Curie–Weiss-type behavior is observed in the magnetic susceptibility. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Fe2+ ions.

The new oxyarsenate Li{sub 0.5}Ni{sub 0.25}TiOAsO{sub 4} has been synthesized and studied by a combination of X-ray powder diffraction, neutrons powder diffraction and vibrational spectroscopy. Li{sub 0.5}Ni{sub 0.25}TiOAsO{sub 4} crystallizes in the monoclinic P2{sub 1}/c space group with the unit cell parameters: a = 6.5854(3) A, b = 7.4665(4) A, c = 7.4969(4) A, {beta} = 89.884(6){sup o}, V = 368.62(1) A{sup 3} and Z = 4. The structure has been determined at room temperature from neutrons diffraction by the Rietveld method analysis. It is formed by a 3D network of TiO{sub 6} octahedra and AsO{sub 4} tetrahedra sharing corners. Structural refinement shows a partial and a statistical occupancy of 2a and 2b sites by Li{sup +} and Ni{sup 2+} ions. TiO{sub 6} octahedra are linked together by corners and form infinite chains along c-axis. Raman and infrared studies confirm the existence of -Ti-O-Ti- chains. Diffuse reflectance spectrum indicates the presence of octahedrally coordinated Ni{sup 2+} ions.

A new titanium oxyphosphate Mg{sub 0.50}TiO(PO{sub 4}) has been synthesized and characterized by several physical techniques: X-ray diffraction, {sup 31}P MAS-NMR, Raman diffusion, infrared absorption and diffuse reflectance spectroscopy. It crystallizes in the monoclinic system with unit cell parameters: a = 7.367(9), b = 7.385(8), c = 7.373(9) A, {beta} = 120.23(1), with the space group P2{sub 1}/c (no. 14), Z = 4. The crystal structure has been refined by the Rietveld method using X-ray powder diffraction. The conventional R indices obtained are R {sub wp} = 0.138, R {sub p} = 0.096 and R {sub B} = 0.0459. The structure of Mg{sub 0.50}TiO(PO{sub 4}) consists of infinite chains of corner-shared [TiO{sub 6}] octahedra parallel to the c-axis, crosslinked by corner-shared [PO{sub 4}] tetrahedra. These infinite chains have alternating short (1.74 A) and long (2.26 A) Ti-O bonds and are similar to those found in titanium oxyphosphate M{sup II} {sub 0.50}TiO(PO{sub 4}) (M{sup 2+} = Fe{sup 2+}, Co{sup 2+}, Ni{sup 2+}, Cu{sup 2+}, Zn{sup 2+}). The magnesium atom is located in an antiprism between two [TiO{sub 6}] octahedra. {sup 31}P MAS NMR showed only a single {sup 31}P resonance line, in a good agreement with the crystal structure. Raman andmore » IR spectra show strong bands respectively at 765 and 815 cm{sup -1}, attributed to the vibration of -Ti-O-Ti-O- bonds in the infinite chains. The gap due to the Oxygen-Titanium(IV) charge transfer is 3.37 eV.« less

The thermal study of Cu 0.50 TiO(PO 4 ), by X-ray diffraction and DSC, shows a phase transition α → β with a hysteresis (∼600 °C during heating; ∼300 °C during cooling). Single crystals have been obtained for the α-phase but the β-phase can only be stabilised at room temperature as a powder mixture with α. Structural characterization of the β-variety has been done with diffraction data (X-ray Cu Kα 1 and neutrons) using a powder rich in β-phase (α(20%) + β(80%)). A monoclinic cell ( a = 7.1134(7) A; b = 7.7282(7) A; c = 7.3028(7) A; β =119.30(1)°; V = 350.1(1) A 3 ) has been found for β-phase, space group P 2 1 / c . An “ ab initio ” structure determination has been done, and the Rietveld refinement leads to cR wp = 0.150 and R B = 0.041. The results from the X-ray data were confirmed by refinements from neutron data. Similarly to the α-phase, the structure of β-Cu 0.50 TiO(PO 4 ) can be described as a TiOPO 4 framework constituted of chains of tilted corner-sharing [TiO 6 ] octahedra running parallel to the c axis and cross linked by [PO 4 ] tetrahedra. Ti atoms are displaced from the centres of the octahedral units, leading to long (2.27 A) and short (1.73 A) Ti–O(1) bonds. The [CuO 6 ] octahedra exhibit a typical Jahn–Teller distorted coordination with four short equatorial Cu–O bonds (2 × 1.93 A and 2 × 2.06 A), and two longer apical Cu–O bonds (2 × 2.33 A). The two longer Cu–O bonds are almost parallel to the b axis. The transition from the α to the β-phase is characterized by a “rocking” of the Jahn–Teller elongation from the ( a , c ) plane to the b direction accompanied by a relatively strong expansion of the cell volume.

The room-temperature crystal structure of a new Cu(II) oxyphosphate—α Cu0.50IITiO(PO4)—was determined from X-ray single crystals diffraction data, in the monoclinic system, space group P21/c. The refinement from 5561 independent reflections lead to the following parameters: a=7.5612(4)A, b=7.0919(4)A, c=7.4874(4)A, β=122.25(1)°, Z=4, with the final R=0.0198, wR=0.0510. The structure of α Cu0.50IITiO(PO4) can be described as a TiOPO4 framework constituted by chains of tilted corner-sharing [TiO6] octahedra running parallel to the c-axis and cross linked by phosphate [PO4] tetrahedra, where one-half of octahedral cavities created are occupied by Cu atoms. Ti atoms are displaced from the center of octahedra units in alternating long (2.308 A) and short (1.722 A) Ti–O(1) bonds along chains. Such O(1) atoms not linked to P atoms justify the oxyphosphate formulation α Cu0.50TiO(PO4). The divalent cations Cu2+ occupy a Jahn–Teller distorted octahedron sharing two faces with two [TiO6] octahedra. EPR and optical measurements are in good agreement with structural data. The X-ray diffraction results are supported by Raman and infrared spectroscopy studies that confirmed the existence of the infinite chains –Ti–O–Ti–O–Ti–. α Cu0.50TiO(PO4) shows a Curie–Weiss paramagnetic behavior in the temperature range 4–80 K.

A new Nasicon phosphates series [Na3+xCr2−xCox(PO4)3(0⩽x⩽1)] was synthesized by a coprecipitation method and structurally characterized by powder X-ray diffraction. The selected compound Na3.5Cr1.5Co0.5(PO4)3 (x=0.5) crystallizes in the R3c space group with the following hexagonal unit-cell dimensions: ah=8.7285(3) Å, ch=21.580(2) Å, V=1423.8(1) Å3, and Z=6. This three-dimensional framework is built of PO4 tetrahedra and Cr∕CoO6 octahedra sharing corners. Na atoms occupy totally M(1) sites and partially M(2) sites.

The single crystals of lanthanum metaphosphate MLa(PO3)4 (M=Na, Ag) have been synthesized and studied by a combination of X-ray crystal diffraction and vibrational spectroscopy. The sodium and silver compounds crystallize in the same monoclinic P21/n space group ( C 2 5 h factor group) with the following respective unit cell dimensions: a = 7.255 ( 2 ) , b = 13.186 ( 3 ) , c = 10.076 ( 2 ) A , β = 90.40 ( 2 ) ° , V = 963.0 ( 4 ) A 3 , Z = 4 and a = 7.300 ( 5 ) , b = 13.211 ( 9 ) , c = 10.079 ( 7 ) A , β = 90.47 ( 4 ) ° , V = 972.09 ( 12 ) A 3 , Z = 4 . This three-dimensional framework is built of twisted zig-zag chains running along a direction and made up of PO4 tetrahedra sharing two corners, connected to the LaO8 and NaO7 or AgO7 polyhedra by common oxygen atoms to the chains. The infrared and Raman vibrational spectra have been investigated. A group factor analysis leads to the determination of internal modes of (PO3)− anion in the phosphate chain.

The existence of isostructural titanates with a composition corresponding to the formula MLi2Ti6O14 has been evidenced in the ternary oxide systems MO–Li2O–TiO2 (M = Sr, Ba, Pb). Single crystals of these compounds have been grown by the flux method using LiBO2 as a high-temperature solvent. The structure, as determined by single crystal X-ray diffraction is orthorhombic (space group Cmca (no. 64), Z = 8) with (i) a = 16.570(5) A, b = 11.150(2) A, c = 11.458(2) A, V = 2116.9(8) A3, R1 = 0.039, w R2 = 0.087 for SrLi2Ti6O14; (ii) a = 16.577(1) A, b = 11.273(1) A, c = 11.581(1) A, V = 2164.2(5) A3, R1 = 0.018, w R2 = 0.047 for BaLi2Ti6O14 and (iii) a = 16.649(1) A, b = 11.146(1) A, c = 11.494(1) A, V = 2132.9(5) A3, R1 = 0.033, w R2 = 0.078 for PbLi2Ti6O14. A three-dimensional framework of edge and corner sharing TiO6 octahedra sets up the crystal structure. Lithium occupies the tetrahedral vacancies, while M atoms are located at 11-oxygen coordinated sites.

Li(1� 2x)NixTiO(PO4) oxyphosphates with 0 � x � 0.10 crystallize in the orthorhombic system with the space group Pnma, those with 0.10 < x � 0.25 crystallize in the monoclinic system with the space group P21/c and compositions with 0.25 < x < 0.50 present a mixture of the limit of the solid solution Li0.50Ni0.25TiO(PO4) and Ni0.50TiO(PO4). The structure of the compositions 0 � x � 0.25 is based on a three-dimensional anionic framework constructed of chains of alternating TiO6 octahedra and PO4 tetrahedra, with the lithium and nickel atoms in the cavities in the framework. The dominant structural units in the compositions are chains of tilted corner-sharing TiO6 octahedra running parallel to one of the axis. The oxygen atoms of the shared corners, not implied in (PO4) tetrahedra, justify the oxyphosphate designation. Titanium atoms are displaced from the geometrical center of the octahedra resulting in alternating long (� 2.25 A ˚ ) and short (� 1.71 A ˚ ) Ti‐O(1) bonds. The four remaining Ti‐O bond distances have intermediate values ranging from 1.91 to 2.06 A ˚ .

Li(1−2x)NixTiO(PO4) oxyphosphate powders were prepared from dilute solutions of NiCl2⋅6H2O, Li2CO3, (NH4)2HPO4, and TiCl4 in ethanol. The final temperature was 850 °C. Li(1−2x)NixTiO(PO4) oxyphosphates with 0≤x≤0.10 crystallize in the orthorhombic system with space group Pnma, while those with 0.101/c.

A new strontium lithium titanate with composition SrLi2Ti6O14 has been discovered in the ternary system SrO - Li2O - TiO2. Single crystals of this compound have been grown by the flux method. The structure of SrLi2Ti6O14 has been solved using X-ray data (Mo-Kα radiation, orthorhombic, space group Cmca, Z = 8, with a = 16.570(5), b = 11.150(2), c = 11.458(2) Å , R1 = 0.039 (wR2 = 0.087)). The crystal structure is built by edge and corner sharing TiO6 octahedra which form layers parallel to the (100) plane. Consecutive layers [deduced from a mirror plane parallel to (100)] are linked by common corners in the a direction. Lithium atoms in tetrahedral coordination occupy vacancies of the framework of titanium octahedra, while strontium atoms lie in 11-coordinated sites between two successive layers.

Vitreous and relevant crystalline polymorphs of P2O5 have been synthesised and characterised by X-ray diffraction and Raman scattering spectroscopy. On the basis of the crystallographic data of single crystals of the three varieties H-P2O5, O-P2O5 and O'-P2O5, the interpretation of vitreous P2O5 Raman spectrum was given taking into consideration the short and intermediate range order. It inferred that the intermediate range order in v-P2O5 can mainly be described in terms of a mixture of both high temperature modifications, with however predominance of O'-P2O5. This hypothesis has been substantiated by in situ Raman study of v- P2O5 recrystallisation. 1. INTRODUCTIONDuring the last five decades, various crystallographic and crystal chemical studies, conducted in different Laboratories, have soundly established the existence of three crystalline forms and a vitreous variety for the diphosphorus pentaoxide [1-5]. However, a closer examination of the published work, indicates that the structure of vitreous P2O5 has not been sufficiently studied yet. Therefore, in an attempt to find out whether there is any intimate relationship between v- P2O5 structure and the crystalline modifications, H- P2O5 [6,7], O- P2O5 [1,8] and O'- P2O5 [4,9], this question will be approached with a view toward

An efficient new scintillator that contains lithium, gadolinium, and boron, all three of which possess large neutron capture cross-section isotopes for highly exothermic reactions, has been recently developed. The homologous yttrium material was also investigated. These compounds of composition Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd, Y) can be activated by Ce/sup 3+/. The synthesis of powders was carried out by high-temperature solid-state reaction from the starting materials LiOH, H/sub 2/O, H/sub 3/BO/sub 3/, Gd/sub 2/O/sub 3/, or Y/sub 2/O/sub 3/, and Ce(NO/sub 3/)/sub 3/, 6H/sub 2/O of purity /spl ges/99.99%, under a flow of argon/H/sub 2/ (5%). Under ultraviolet excitation, they show a broadband emission peaking at 390 nm. The gadolinium emission lies near the maximum of a 4f-5d Ce/sup 3+/ absorption band, so efficient Gd/sup 3+/-Ce/sup 3+/ transfer occurs. Ce/sup 3+/:Li/sub 6/R(BO/sub 3/)/sub 3/ (R=Gd, Y) crystals were grown by the Czochralski method in a resistance heating furnace using a conical vitreous carbon crucible of 150 cm/sup 3/ under deoxygenated pure argon. Monocrystalline boules as large as 3 cm diameter and 6 cm length have been obtained. The interest of these new materials is the high scintillation efficiency-as much as six times that of Li-glass scintillators for the Gd material. Moreover, these scintillators offer the ability to tailor their response to the neutron spectrum by varying the isotopic composition of the key constituents [lithium, gadolinium (yttrium), boron].

The structure of Li3Gd(BO3)2 has been solved by X-ray diffraction study on single crystal. This novel borate crystallizes in the monoclinic system with the P21/c space group (Z=4). The cell parameters are respectively equal to a=8.724(2), b=6.425(2), c=10.095(2) A and β=116.85(2)°. Refinements of 110 parameters using 2924 independent reflections having I>2σ(I) converged to R1=0.028 (wR2=0.058). The structure of Li3Gd(BO3)2 is made up of double layers of eightfold coordinated Gd atoms parallel to the (bc) plane. They are linked by respectively three- and four-coordinated boron and lithium atoms. The structure is compared to that of the homologous sodium compounds, Na3Ln(BO3)2 (Ln: La, Nd), in which LnO8 polyhedra also form a bi-dimensional array.

A new type of lithium rare earth oxyborate of formula Li2Ln5O4(BO3)3 (Ln=Yb, Lu) has been discovered in the ternary phase diagrams Li2O–Ln2O3–B2O3. Single crystals of Li2Yb5O4(BO3)3 were grown by the flux method. The structure of this oxyborate was solved from a data collection with a four circle automatic diffractometer and with MoKα radiation. The cell is monoclinic (space group P21/m, Z=2) with a=10.095(2) A, b=3.519(2) A, c=15.647(11) A, β=105.45(3)°, V=535.7(5) A−3. Refinement of 86 parameters using 3298 independent reflections having intensity I>2σ(I) led to R=0.037 (wR=0.091). The structure of Li2Yb5O4(BO3)3 is made up of a bidimensional framework of edge or corner-sharing YbO7 polyhedra parallel to the (10 1 ) plane and connected by three-coordinated boron atoms and lithium ions. It can also be described as a bidimensional assembly of OYb4 tetrahedra, ((Yb10O8)14+)n, separated by borate groups and lithium coordination polyhedra forming ribbons, ((Li4B6O18)14−)n, along the b direction. The presence of oxygen atoms sharing only Yb polyhedra justifies the oxyborate label.

In the context of a detailed investigation of the luminescent properties of the Na 2− x Ag x ZnP 2 O 7 compounds, the structure of the pure sodium phosphates was “revisited.” The crystal structure of Na 2 ZnP 2 O 7 has been determined by X-ray diffraction using single crystals. A new model explaining the actual large unit cell ( a = b =2177.1(3) pm, c =1028.5(2) pm, P4 2 / n , Z =32) was determined by assuming the existence of twins. The structure is made up of [ZnP 2 O 7 ] layers consisting of corners sharing [P 2 O 7 ] groups and [ZnO 4 ] tetrahedra, and the sodium atoms are located between the layers in 7- or 8-fold coordinated sites. This model is discussed with respect to the crystal chemistry of the monovalent cation zinc phosphate.

The crystal structure of Na 3 Bi 5 (PO 4 ) 6 was solved using the single-crystal X-ray diffraction technique. The structural refinement has led to a reliability factor of R 1 =0.0257 ( wR 2 =0.0533) for 428 independent reflections. This compound was found to crystallize in the cubic system (space group I 43 d ) with eulytite structure and the lattice parameters: a =10.097 (4) A, V =1029.38 A 3 , Z =2, D calc. =5.43 g cm −3 ( D exp. =5.32(5) g cm −3 ). The structure is characterized by the existence of one single general position (48a) for oxygen anions and two distinguished positions (16c) occupied by Na + and Bi 3+ cations, respectively. The site occupation factors are equal to 3/8 and 5/8 for sodium and bismuth, respectively. Although all PO distances are identical (1.529(4) A), the OPO angles ranging from 108.06 (15) to 112.32 (31)°, show that [PO 4 ] 3− are rather distorted. Both sodium and bismuth cations are located in octahedral sites with corresponding mean distances of NaO and BiO equal to 2.428 and 2.386 A, respectively. As expected from the close values of the ionic radii of Na + and Bi 3+ , these distances lie in the same range.

Ba 3 Bi(PO 4 ) 3 crystallizes with the eulytite structure and the cubic space group I 4 3 d . X-ray crystallography has allowed us to determine the following crystal data: a = 10.5036(4) A, V = 1158.8 A 3 , Z = 4, D cal = 5.19 g/cm 3 , D exp = 5.02 g/cm 3 . The structure was solved on a single crystal, using 343 independent reflections, with R1 = 0.0379 (wR2 = 0.0752). It could be viewed as built up from independent [PO 4 ] 3– tetrahedra, lying along rods parallel to the axis and to [001]. The rods are arranged in a manner to delimit pairs of irregular pentagonal tunnels. In addition to two oxygen sites identified in the title structure, as previously reported for other compounds, two different sites were refined for barium and bismuth contrary to what has been reported in equivalent eulytite compounds.

The luminescence of silver(I) ions was investigated in diphosphate of compositions Na 2− x Ag x ZnP 2 O 7 . The [P 2 O 7 ] groups share corners with [ZnO 4 ] tetrahedra in a layer arrangement. The Na/Ag atoms are located between layers in distorted oxygenated cubic sites sharing faces—with short intermetallic distances—or edges. Two luminescent centers were detected and attributed, respectively, to single Ag + and Ag + –Ag + pairs. The luminescent parameters are discussed with respect to the symmetry of the silver sites and of the ionocovalent character of the silver oxygen bonds

Centimeter-sized single crystals of pure and Pr 3+ -doped Cs 4 PbBr 6 were successfully grown using a high-temperature solution (HTS)-based vertical Bridgman–Stockbarger method in silica ampoules sealed under Ar gas. The single crystals are bright orange transparent, non hygroscopic, with a low phonon energy and a wide transparency in the middle infrared (MIR) region. Pr 3+ ions can be dissolved into Cs 4 PbBr 6 crystals, resulting in broad MIR absorption bands. We present the characterization of the single crystals by means of Raman, visible, Fourier-transform infrared (FT IR) and emission spectroscopies.

Crystals of Rb 2 KInF 6 :Tb 3+ with elpasolite structure have been prepared by the Bridgman method. Absorption, wide range luminescence, high resolution emission, excitation and luminescence decay measurements have been carried out at low and room temperature in order to study the environments of Tb 3+ ions and their optical properties. An O h site of Tb 3+ ions (octahedral TbF 6 3− ; units) has been found and the identification and assignments of the pure magnetic-dipole transitions split out of the Tb 3+ 5 D 4 → 7 F 6 , 7 F 5 , 7 F 4 , 7 F 3 and 5 D 3 → 7 F 6 , 7 F 5 , 7 F 4 transitions have been achieved assuming a thermal equilibrated set of crystal-field sublevels and comparing with the literature data in chloride and fluoride elpasolites; a C 2v distortion of the octahedral symmetry has been detected at low temperature. Some experimental results could suggest the presence of a small concentration of other sites of Tb 3+ with a symmetry lower than O h . Energy transfer between the two sites could also be suggested. Finally, an up-conversion process by means of sequential two-photon absorption ( 7 F 6 → 5 D 4 and 5 D 4 → above 5 D 3 ) has been demonstrated.

A new family of lithium rare earth oxyborates of formula LiLn6O5(BO3)3 (Ln=Pr–Tm) has been discovered in the ternary-phase diagrams Li2O–Ln2O3–B2O3. Single crystals of LiGd6O5(BO3)3 were grown by the flux method. The structure of the oxyborate was solved using a data collection with a four-circle automatic diffractometer (CAD-4) and with MoKα radiation. The cell is monoclinic (space group P21/c, Z=4) with a=8.489(4) A, b=15.706(3) A, c=12.117(6) A, β=132.27(2)°, and V=1195(1) A3. Refinement of 198 parameters using 4402 independent reflections having intensity I>3σ(I) led to R=0.037 (wR=0.087). The structure of LiGd6O5(BO3)3 can be described as a three-dimensional framework, (Gd6O14)10−, of Gd polyhedra connected by common edges and corners, forming cavities where Li and B atoms are inserted. Some oxygen atoms share only Gd polyhedra, justifying the oxyborate label.

The structure of the oxyphosphate Ni0.50TiO(PO4) has been determined ab initio from conventional X-ray powder diffraction data by the “heavy atom” method. The cell is monoclinic (space group P21/c, Z=4) with a=7.3830(5) Å, b=7.3226(5) Å, c=7.3444(5) Å, and β=120.233(6)°. Refinement of 46 parameters by the Rietveld method, using 645 reflexions, leads to cRwp=0.152, cRp=0.120, and RB=0.043. The structure of Ni0.50TiO(PO4) can be described as a TiOPO4 framework constituted by chains of tilted corner-sharing TiO6 octahedra running parallel to the c axis, crosslinked by phosphate tetrahedra and in which one-half of octahedral cavities created are occupied by Ni atoms. Ti atoms are displaced from the center of octahedra units in alternating long (2.231) and short (1.703 Å) Ti–O bonds along chains.

International audience; In this paper, we present the results of our attempt to grow NaBiW2O8 (NBW) and Na5B2P3O13 (NBP) crystals by the heat exchanger method (HEM). This method is slightly different from the Bridgman technique: the crucible is kept fixed in the setup and the center of the crucible bottom is cooled by a variable helium gas flow. It allows very good control of the growth rate and minimizes parasitic crystallization at the crucible walls. First experiments for growing these two materials by the HEM technique have shown very promising results with single-crystal sizes of few cubic centimetres..

Single crystals of Pb(H2PO4)2 were grown under hydrothermal conditions. X-ray crystallography showed that the title compound crystallizes in the triclinic system with space group P1 and lattice parameters a = 7.812, b = 8.311, c = 5.859 A, α = 108.23°, β = 96.85°, γ = 108.62°, Z = 2, and ρcal = 4.011 g·cm−3. The structure was solved from 3705 independent reflections with R = 0.043 (wR = 0.11). It can be regarded as made of independent [PO4] tetrahedra. Two apices of each [PO4] tetrahedron are connected to two H atoms to form [H2PO4]− anions arranged in a way to delimit large and distorted cavities occupied by lead cations. The resulting arrangement could be seen as made of infinite strips, developing along [001] and connected through hydrogen bonds.

Copper deficiency is studied in YBa 2 Cu 3 O 7− x phase. We compare polycrystals formed by sintering with textured and single crystals. The experimental method uses electron probe micro-analysis and X-ray structural determinations on single crystals. We show that YBa 2 Cu 3 O 7− x phase accommodates Cu deficiency up to several percent. Copper vacancies are located at the Cu(1) site (in the chains). Copper deficiency is evidenced when a liquid phase is involved in the chemical process. The implications of copper vacancies on the physical properties has probably to be reconsidered in future.

Summary The titanium phosphate Na 4 Ca 0.5 Ti(PO 4 ) 3 crystallizes in the trigonal space group R32 (a h = 9.008 ± 0.002 A, c h = 21.814 ± 0.003 A and Z = 6). Its structure belongs to the nasicon type family. The titanyl phosphate Ni 0.5 TiOPO 4 crystallizes in a monoclinic unit cell, P2 I ,/c, (a = 7.383 ± 0.001 A, b = 7.323 ± 0.001 A, c = 7.344 ± 0.001 A, β = 120.23 ± 0.01° and Z = 4). The structure of these two compounds is based on a three-dimensional framework built of TiO 6 octahedra and PO 4 tetrahedra. The PO 4 tetrahedra are isolated in both Na 4 Ca 0.5 Ti(PO 4 ) 3 and Ni 0.5 TiOPO 4 . The TiO 6 octahedra are isolated in the former and linked together by “titanyl” oxygen atoms to form -Ti-O-Ti-O- infinite chains in the latter. These structural data are confirmed by the Raman spectroscopy study.

Crystals of Ce-doped BaThF 6 have been grown using the Bridgman technique. They show scintillation properties with a fast decay ( τ = 16.5 ns). Departures from stoichoimetry caused by the high vapour pressure of ThF 4 influence the position of the Ce 3+ emission band.

The title compound is synthesized by precipitation from an aqueous solution of Mn(NO3)2, CsCl, and NH4H2PO4 followed by heating in air (progressive heating 200700 °C with intermediate grinding).

A new member of the A{sub 2}MP{sub 2}O{sub 7} diphosphate family, Cs{sub 2}MnP{sub 2}O{sub 7}, has been synthesized and structurally characterized. The crystal structure was determined by single crystal X-Ray diffraction. Cs{sub 2}MnP{sub 2}O{sub 7} crystallizes in the orthorhombic system, space group Pnma ( Music-Sharp-Sign 62), with the unit cell parameters a=16.3398(3), b=5.3872(1), c=9.8872(2) A, Z=4 and V=870.33(3) A{sup 3}. The structure parameters were refined to a final R{sub 1}/wR{sub 2}=0.0194/0.0441 for 1650 observed reflections. The 2D framework of Cs{sub 2}MnP{sub 2}O{sub 7} structure consists of P{sub 2}O{sub 7} and MnO{sub 5} units. The corner-shared MnO{sub 5} and P{sub 2}O{sub 7} units are alternately arranged along the b axis to form [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains. These chains are interconnected by an oxygen atom to form sheets parallel to the (b, c) plane. The cesium atoms are located between the sheets in 9- and 10-fold coordinated sites. The infrared and Raman vibrational spectra have been investigated. A factor group analysis leads to the determination of internal modes of (P{sub 2}O{sub 7}) groups. UV-visible spectrum consists of weak bands, between 340 and 700 nm, assigned to the forbidden d-d transitions of Mn{sup 2+} ion, and of a strong band around 250more » nm, attributed to the O--Mn charge transfer. - Graphical abstract: Structure of Cs{sub 2}MnP{sub 2}O{sub 7}: The 2D structure of Cs{sub 2}MnP{sub 2}O{sub 7} is built from P{sub 2}O{sub 7} diphosphate groups and MnO{sub 5} square pyramids which share corners and form [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains along b axis. These chains are interconnected by an oxygen atom to form wavy (MnP{sub 2}O{sub 7}){sup 2-} sheets parallel to the (b, c) plane. The cesium ions are located between these sheets in the inter-layers space, in zigzag positions. Highlights: Black-Right-Pointing-Pointer A new diphosphate, Cs{sub 2}MnP{sub 2}O{sub 7}, has been synthesized and structurally characterized. Black-Right-Pointing-Pointer The structure consists of a 2D framework built up from (MnP{sub 2}O{sub 7}) sheets. Black-Right-Pointing-Pointer The sheets consist of [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains formed by P{sub 2}O{sub 7} units and MnO{sub 5} square pyramids. Black-Right-Pointing-Pointer A factor group analysis leads to the determination of internal modes of (P{sub 2}O{sub 7}) groups. Black-Right-Pointing-Pointer UV-visible spectrum consists bands assigned to d-d transitions of Mn{sup 2+} ion and to O--Mn CT.« less

The crystal structure of o-modification of diphosphorus pentaoxide was refined at 295 K. It consists of a network of [PO4] tetrahedra linked by three common apices. Moreover, this o-modification of P2O5is also found to crystallize in the orthorhombic system with the space groupFdd2 and the lattice parametersa= 16.314(2) A,b= 8.115(3) A,c= 5.265(9) A,Z= 8, andDcalc= 2.705 (g · cm−3). The main value of the P–O length is estimated to be 1.543 A. As expected, the nonbridging P–O bonds, equal to 1.445 A, are shorter than the bridging ones which average 1.582 A. The structure parameters are refined to a finalRof 0.0351 (wR= 0.0643) for 550 independent reflections [I> 3σ(I)]

The home-made heat exchanger method (HEM) apparatus has been adapted to the growth of NaMgF 3 ingots. By unseeded crystal growth using presynthesized NaMgF 3 the structure was maintained during growth. Twinning introduced by the high-temperature phase transition is observed in the crystal. Studies on the crystals, at high temperature, by optical microscopy, calorimetry and Raman scattering, show a unique phase transition, from orthorhombic (Pbnm) to cubic (Pm3m) structure, at about 770°C.

Resume X-ray diffraction, differential thermal analysis, polarized light microscopy, and dielectric measurements have been used to study phase transitions and solid solutions in the K3MO3F3–A3MO3F3(A= Rb, Na;M= Mo, W) systems. K3MO3F3–Na3MO3F3(M= Mo, W) systems show two solid solutions; the first (SSI) nearx= 0 (K3−xNaxMO3F3) involves only one transition atTCwhich is practically independent of composition. The sharp transition atT1(

Two new phosphates Fe0.5TiO(PO4) and Fe0.5Ti2(PO4)3 have been prepared and characterised by X-ray diffraction, Mossbauer spectroscopy and magnetic measurements...

Ce3+ luminescence was investigated in elpasolite fluoroindates A2BInF6 (A = K, Rb; B = Na, K). All A2BInF6:Ce3+ have been synthesized by solid state reactions from stoichiometric mixtures in sealed gold tubes at 700°C. Transparent colourless Rb2KInF6:Ce3+ crystals were grown by Bridgman method in 10% Rh-Pt crucibles sealed under dry argon atmosphere. At room temperature Rb2KInF6:Ce3+ presents a blue-green broad-band emission when excited with a 315 nm UV radiation. This emission can be ascribed to the Ce3+ ions in In3+ site. Two other emissions in the blue and UV can be assumed to originate from Ce3+ ions located in the 6 coordinated potassium and 12 coordinated rubidium sites. Under a steady 315 nm UV excitation the main blue-green Ce3+ emission decreases progressively, giving rise to a new emitting centre which exhibits a red emission under 255 nm excitation. This phenomenon is optically reversible and moreover the original state can be thermally regenerated. An hypothesis based on the ln(III)-...

Absorption as well as fluorescence measurements on CsCdBr 3 :Pr 3+ permit us to construct an energy level scheme for the main site occupied by the rare earth corresponding to the [RE 3+ -Vacancy-RE 3+ ] pair entity. A simulation of these levels made on the basis of a C 3v symmetry for the point site gives a low r.m.s. deviation. The crystal field parameters (CFPs) vary smoothly when compared with other rare earths embedded in the same matrix.

International audience; Tetragonal Tungsten Bronze Ferroelectrics (TTB) are currently revisited for the elaboration of new multifunctional materials. Recent studies on Ba2LnFeNb4O15 ceramics (Ln=Nd, Sm and Eu) demonstrated that these materials display both ferroelectric and ferromagnetic behaviors at room temperature due to the presence of barium hexaferrite as a secondary phase. In this paper, we report for the first time the growth of Ba2LnFeNb4O15 single crystals (Ln=La, Pr, Nd, Sm and Eu) from high temperature solution using LiBO2 flux. Inclusion free millimeter-sized single crystals were successfully grown. Structural and dielectric characterizations were performed and chemical analysis confirmed that the TTB matrix is reluctant to accommodate small rare earth as it was observed for ceramics. A paramagnetic behavior was observed for all compositions, which corroborates the composite nature of the TTB ceramic multiferroics at room temperature, while dielectric measurements on Ln=La and Pr crystals confirmed their relaxor behavior.

The crystal structures of the ordinary pressure forms of indium digermanate In2Ge2O7 and disilicate In2Si2O7 have been studied from X-ray powder diffraction data by Rietveld refinement. They are closely related to that of the thortveitite which crystallizes in the monoclinic system with the space group C2/m and Z = 2. They show luminescence properties below 160 K and 200 K respectively. The luminescence is discussed in terms of crystal structure and compared to that of some other luminescent indium oxides. Strukturuntersuchungen und Lumineszenz von In2Ge2O7 und In2Si2O7 Eine Rietveld-Pulverdiagramm-Methode erlaubt die Bestimmung der genauen Strukturen von Thortveitit verwandten In2Ge2O7 und In2Si2O7 Oxyden (Raumgrupe C2/m, Z = 2). Die Verbindungen wurden unter normalem Druck hergestellt. Die Lumineszenz unter 160 und 200 K sollte die Messung der Umwelt Neutrinobestrahlung erlauben. Sie scheint die Folge eines inneren Ladungstransfers in den Indium Sauerstoff Polyedern zu sein. Die optischen Resultate wurden an Hand der bestimmten Strukturen und der chemischen Bindungen diskutiert und mit Werten fur andere Indiumoxyde verglichen.

The formation of a complete solid solution in the In itx Sc 1 − x BO 3 (0 ⩽ x ⩽ 1) system with a linear variation in unit cell parameters is reported. Crystal growth of the In 0.359 Sc 0.639 Ce 0.002 BO 3 composition was performed by slow cooling of a high temperature solution using LiBO 2 as a solvent in an Ar atmosphere. The luminescence of Ce 3+ in the In x SC 1 − x BO 3 solid solutions and in the as-grown single crystals was investigated. The influence of In content on the luminescent intensity of Ce 3+ is discussed in relation to heat treatment conditions.

Structural, ferroelectric, pyroelectric, and optical properties of ceramics and crystals of BaAl2O4 have been investigated. A refinement of the atomic positions has been carried out from the X-ray powder data. BaAl2O4 shows anomalous behavior of the dielectric and pyroelectric properties: the dielectric constant e′r is very weak; its maximal value at Curie temperature for a crystal oriented along the hexagonal c-axis is about 15 and that of a ceramic of compactness 0.89 is around 7.5. The Curie-Weiss constant is relatively weak (C = 125). The behavior of the spontaneous polarization Ps is unexpected with respect to that of classical ferroelectric materials: Ps increases with decreasing temperature from Tc and decreases again after having reached a maximum at 200 K. A model based on ferrielectric behavior and supported by the Landau equation has been proposed. La structure et les proprietes ferroelectriques, pyroelectriques et optiques de ceramiques et de cristaux du compose BaAl2O4 ont ete etudiees. Un affinement des positions atomiques a ete entrepris a partir du spectre de diffraction X sur poudre. BaAl2O4 presente un comportement anormal des proprietes dielectriques et pyroelectriques: la constante dielectrique e′r est faible, sa valeur maximale a Tc est voisine de 15 pour les cristaux et de 7,5 pour des ceramiques de compacite 0,89. La constante de Curie est aussi relativement faible (C = 125). Le comportement de la polarisation spontanee Ps differe de celui des materiaux ferroelectriques "classiques": Ps augmente lorsque T decroit en-dessous de Tc pour atteindre un maximum a T = 200 K suivi d'une decroissance. Un modele de comportement ferrielectrique s'appuyant sur la relation de Landau pourrait justifier les proprietes observees.

Single crystals of indium tungstate In 6 WO 12 have been grown by chemical vapor deposition using TeCl 4 as a transport agent. Isometric as well as octahedral-shaped transparent crystals are obtained with a size attaining 2 mm. The luminescence of both single crystals and powder samples has been investigated. On the basis of a comparison with Y 6 WO 12 , the green emission is ascribed to charge transfer transitions within isolated octahedral tungstate groups.

The crystal structure of indium titanate (In[sub 2]TiO[sub 5]) has been refined from X-ray powder diffraction data by Rietveld refinement. In[sub 2]TiO[sub 5] is isostructural with In[sub 2]VO[sub 5]. It crystallizes in the orthorhombic space group Pnma with a = 7.2418(7) [angstrom], b = 3.5018(3) [angstrom], c = 14.890(2) [angstrom], V = 377.6(4) [angstrom][sup 3] and Z = 4. The final reliability factors were R[sub p] = 8.5%, R[sub wp] = 11.1% and R[sub I] = 5.6%. In[sub 2]TiO[sub 5] shows luminescent properties below 220 K. The luminescence is discussed in terms of crystal structure and compared to that of some other luminescent titanates and indates.

The sodium titanium phosphate Na5Ti(PO4)3 crystallizes in the trigonal space group R32 (a = 9.0607(2) A, c = 21.734(1) A, V = 1545.3 A3, dm = 2.84(2), dc = 2.89 Mg · m-3, Z = 6). R = 0.022 and Rw = 0.023 for 831 reflections. The structure belongs to the Nasicon-type family and is characterized by a 2-2 titanium-sodium ordering along the c axis. The four crystallographically independent sodium atoms show coordination numbers 6 and 8. The cell parameters and the cationic distribution are consistent with the rules governing the structural evolution of such types of material.

Trivalent transition ions associate in pairs when doped in CsCdBr 3 crystals. Using high resolution absorption and emission spectroscopy, we have measured the energy levels of Pr 3+ : CsCdBr 3 and determined their associated irreducible representations. From Zeeman measurements we obtained the g factor for the 1 D 2 multiplet ( g ⌈ = 0.9; g ⊥ = 0) and the predictions of a sim crystal field model show that Pr 3+ ions see mainly an octahedral contribution, plus a small C 3v distortion. We also use these measurements to determine a value of the hyperfine interaction constant A J ( 1 D 2 of 440 +- 150 MHz which is smaller than the value previously determined for Pr 3+ : LaF 3 .

The growth of CaClF:Sm 2+ single crystals has been investigated in connection with spectral hole burning phenomena. CaClF:Sm 2+ has been grown by slow cooling of a high temperature solution using CaCl 2 as solvent. X-ray diffraction, optical studies and chemical etching were carried out on the single crystals obtained. The luminescence properties of CaClF:Sm 2+ single crystals have been recorded