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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.

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..

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.

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

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.

International audience; {Tb3}[Sc2−xLux](Al3)O12 crystals have been grown and investigated for the first time for magneto-optical applications. Tb3Al5O12 exhibits the best magneto-optical features; however, its incongruent melting nature has led to the industrial use of Tb3Ga5O12. Tb3Sc2Al3O12 had been proposed as an alternative to Tb3Al5O12, but unfortunately its growth also presents several drawbacks. The present investigation shows that by the isovalent substitution of Sc3+ by Lu3+ in the octahedral site of the garnet structure, it is possible to improve the growth characteristics while preserving the superior magneto-optical properties. We demonstrate that {Tb3}[Sc2−xLux](Al3)O12 crystals show a higher visible transparency and a larger Faraday rotation than Tb3Ga5O12 crystals. {Tb3}[Sc2−xLux](Al3)O12 is therefore a very promising material in particular for new magneto-optical applications in the visible-near IR wavelength region.

International audience; Crystal growth and spectroscopic study of the new compound Yb3+:LiLu(WO4)2 have been undertaken for the first time. Preliminary growth using flux method with Li2W2O7 as solvent allows us to obtain small single crystals. As a promising laser crystal, Yb3+:LiLu(WO4)2 have characteristics of a low concentration quenching effect and low laser threshold owing to the existence of covalent bands in WO4 group. Its absorption peak at 977 nm, corresponding to 2F7/2(1) → 2F5/2(5) transition, is suitable for laser diode pumping. Emission spectrum shows large bands extending from 900 to 1100 nm, five peaks centred respectively at 959, 978, 997, 1025 and 1056 nm are well resolved. The FWHM of the most intense emission band located at 997 nm is about 20 nm. Energy Stark levels are: 0, 201, 469 and 749 cm−1 for the 2F7/2 component and: 10,230, 10,427 and 10,890 cm−1 for the 2F5/2 component. The overall splitting of 2F7/2 ground-state manifold is 749 cm−1, which is larger than that observed in similar systems such as Yb3+:LiLa(WO4)2 (632 cm−1). Such large crystal-field splitting of the 2F7/2 ground-state will be advantageous to lower laser thermal effect and re-absorption losses. As we can see, the stark electronic levels are characterized by relatively large crystal-field splitting favourable to laser crystal applications in the near infrared spectral region.

Sr0.5Zr2(AsO4)3 arsenate was prepared and structurally characterized by powder X-ray diffraction and by Raman and infrared spectroscopies. Its structure, which belongs to the Nasicon-type family, was refined by the Rietveld method in the R-3 space group, from X-ray powder diffraction data. The hexagonal unit-cell parameters were determined to be ah=8.965(2) Å, ch=23.955(6) Å, V=1667.43(6) Å3, and Z=6. The structure is formed by an ionic three-dimensional network of AsO4 tetrahedra and ZrO6 octahedra linked by corners with Sr2+ ions occupying half of the M1 sites in an ordered manner. Raman and infrared spectra were recorded and assignments of the stretching and bending vibrations of the AsO43− tetrahedra were made. The number of the peaks observed is in good agreement with that predicted by the factor-group analysis of the R-3 space group.

International audience; We have extended our research interest on titanium oxyphosphates (MII(TiO)2(PO4)2, with MII = Mg, Fe, Co, Ni, Cu, Zn) to vanadium oxyphosphates MII(VIVO)2(PO4)2 (MII = Co, Ni). For each compound two phases, named α and β according to synthesis conditions, have been stabilized at room temperature, then characterized. The four crystal structures M(VO)2(PO4)2 (α and β for M = Co, Ni) have been determined in monoclinic P21/c space group using X-ray single crystals diffraction data. Structure of the α phase is derived from the Li(TiO)(PO4) (orthorhombic Pnma) and LiNi0.50(TiO)2(PO4)2 (monoclinic P21/c) types, with cell parameters: a = 6.310(1) Å, b = 7.273(1) Å, c = 7.432(1) Å, β = 90.43(1)° for M = Co, and a = 6.297(2) Å, b = 7.230(2) Å, c = 7.421(2) Å, β = 90.36(2)° for M = Ni. Structure of the β phase is derived from the Ni(TiO)2(PO4)2-type (monoclinic P21/c) with cell parameters: a = 7.2742(2) Å, b = 7.2802(2) Å, c = 7.4550(2) Å, β = 120.171(2)° for M = Co, and a = 7.2691(2) Å, b = 7.2366(2) Å, c = 7.4453(2) Å, β = 120.231(2)° for M = Ni. All these structures consist of a three dimensional (3D) framework built up of infinite chains of tilted corner-sharing [VO6] octahedra, cross-linked by corner-sharing [PO4] tetrahedra. The M2+ ion (M = Co, Ni) is located in a triangular based antiprism which shares faces with two [VO6] octahedra. Structural filiation is discussed based on a common structural unit, a sheet where divalent cations M2+ (M = Co, Ni) are inserted. A thermal study of the α ↔ β transition is also presented.

International audience; Single crystals of (1 − x)BaTiO3 + xNaNbO3 (BTNN) for x = 0.84 were obtained by high temperature solution growth using Na2B4O7 as solvent. The room temperature crystal structure of BTNN 16/84-phase was determined from X-ray single crystal diffraction data, in the tetragonal system with space group P4bm. The refinement from 246 independent reflections led to the following parameters: a = b = 5.5845(3) Å, c = 3.9453(2) Å, V = 123.041(11) Å3, Z = 2, with final cRwp = 0.150 and RB = 0.041. The structure of BTNN 16/84-phase can be described as a three-dimensional framework built up from (Nb–Ti)O6 octahedra with Na and Ba in the dodecahedral site of perovskite-like type. Some mm3-sized crystals have been selected and various dielectric measurements (ferroelectric, pyroelectric, and piezoelectric) have been performed. Transition from paraelectric to ferroelectric state at around 460 K has been observed to be in good agreement with ceramics of closer composition. Dielectric, piezoelectric and pyroelectric measurements on crystal confirm the ferroelectric behaviour of BTNN 16/84.

International audience; X-band electron spin resonance (ESR) spectra and fluorescence measurements were performed on Mn-doped Na2ZnP2O7 (NZPO) single crystal synthesized by the Czochralski pulling method and glasses synthesized by the quenching process. For the single crystal, ESR angular dependences were measured in both the zx and xy plans of the NZPO lattice. The fine and hyperfine structure parameters and g-factor values were determined by modelling the experimental spectra. Using the Newman superposition model, the resonating centres in the single crystal and powder (crushed from crystals) samples are assigned to Mn2+ ions substituting for both zinc and sodium. For the glass sample the analysis of the ESR data shows that Mn2+ ions substitute for the Na+ ions. These interpretations are confirmed by the fluorescence measurements with a unique broad red band for the glassy compound and the presence of two emission bands (green and red) in the case of the crystal sample.

International audience; Centimeter-sized single crystals of pure and Pr3+-doped Cs4PbBr6 were successfully grown using a high-temperature solution (HTS)-based vertical Bridgman–Stockbarger method in silica ampoules sealed under Ar gas. The resulting single crystals are bright orange transparent, non-hygroscopic, with a low phonon energy and a wide transparency in the middle infrared (MIR) region. We present the growth conditions together with a characterization of the single crystals by means of calorimetry measurements, room temperature single crystal and powder X-ray diffraction (XRD), Raman, visible and Fourier-transform infrared (FT-IR) spectroscopies. Cs4PbBr6 crystallizes at room temperature in the trigonal space group R-3c, with a = b = 13.7219(2)A˚, c = 17.3153(3)A˚, α = β = 90°, γ = 120° and Z = 6. Pr3+ ions can be dissolved into Cs4PbBr6 crystals, resulting in broad MIR absorption bands.

International audience; Single crystals of NaY(PO3)4 and Ag0.07Na0.93Y(PO3)4 have been synthesized by flux method. These new compounds turned out to be isostructural to NaLn(PO3)4, with Ln=La, Nd, Gd and Er [monoclinic, P21/n, a=7.1615(2) Å, b=13.0077(1) Å, c=9.7032 (3) Å, β=90.55 (1)°, V=903.86(14) Å3 and Z=4]. The structure is based upon long polyphosphate chains running along the shortest unit-cell direction and made up of PO4 tetrahedra sharing two corners, linked to yttrium and sodium polyhedra. Infrared and Raman spectra at room temperature confirms this atomic arrangement. The luminescence of silver ions was reported in metaphosphate of composition Ag0.07Na0.93Y(PO3)4. One luminescent centre was detected and assigned to single Ag+ ions.

The spectroscopic properties of Nd3+ ions in Na3La9O3(BO3)8 single crystals have been studied, for the first time, by using steady-state and time-resolved laser spectroscopy. Site selective laser emission and excitation measurements have been performed to characterize the different sites for the rare-earth in this crystal. These results show the existence of at least two different sites for Nd3+ ions., This work was supported by the Aquitaine-Euskadi Program, Spanish Government MEC (MAT2004-03780), Basque Country University (UPV13525/2001) and the Conseil Régional d’Aquitaine (No. 9004120418171010).

New titanyl phosphate Ti 2 O(H 2 O)(PO 4 ) 2 has been prepared and characterized by X-ray and neutron diffraction, nuclear magnetic resonance, infrared and Raman spectroscopies and thermogravimetric analysis. The crystal structure has been solved from neutron powder diffraction data at 300 K by Rietveld method in P 2 1 space group. The refinement led to satisfactory profile factors ( R p =2.7%, R wp =3.2%) and crystal structure model indicators ( R B =5.8%, R F =3.2%). The cell is monoclinic with a =7.3735 A, b =7.0405 A, c =7.6609 A and β =121.48°, Z =4. The structure can be described as a three-dimensional framework built up by chains of [TiO 5 (OH 2 )] octahedra with alternative short bonds [Ti (1) –O (12) ; Ti (2) –O (12) , 1.88–1.84 A] and long ones [Ti (1) –O W ; Ti (2) –O W , 2.25–2.23 A] along c -axis and connected via [PO 4 ] tetrahedra. Oxygen atom denoted O (12) is only linked to two titanium atoms and Oxygen atom denoted O W is linked to two titanium atoms and two hydrogen atoms. O (12) and O W are not linked to P atoms and justify the titanyl phosphate formulation Ti 2 O(H 2 O)(PO 4 ) 2 . The infrared and Raman spectra presents peaks due to vibrations of Ti–O, P–O and O–H bonds. The 31 P MAS NMR spectrum reveals two 31 P resonance lines, in agreement with the structure which showed two crystallographic sites for phosphorus. The thermogravimetric analysis show that Ti 2 O(H 2 O)(PO 4 ) 2 is thermally stable until 400 °C. Above this temperature, it losses water and decomposes to Ti 5 O 4 (PO 4 ) 4 and TiP 2 O 7 .

The luminescence of Yb3+ in the oxyborate Li2Lu5O4(BO3)3 is reported. At low temperature, in addition to the usual ytterbium infrared emission, this phosphor presents an emission in the ultraviolet ( λ max = 345 nm ) which corresponds to the transition from the charge transfer state (O–Yb) to the 4f levels of Yb3+. The temperature quenching Tq50% is equal to 120 K. The infrared emission studied at room temperature is located between 950 and 1100 nm. Europium emission quenching in the Li2Yb5O4(BO3)3 phase is related to Eu→Yb transfer by cross-relaxation. The reverse Yb→Eu transfer by cooperative sensitization is highlighted in the codoped Li2Lu5O4(BO3)3 compound.

International audience; We report for the first time pulsed laser operation of the Yb-doped Li6Y(BO3)3 (Yb-LYB) crystal in the nanosecond as well as in the femtosecond regime. Pulse durations as short as 355 fs have been obtained in passively mode-locked operation and pulse energies up to 140 μJ in Q-switched operation.

Two new titanates of strontium, lithium and a 3d metal, with the composition SrLiMTi4O11 (M = Cr, Fe), have been discovered. Single crystals were obtained by spontaneous crystallization from a high-temperature solution with LiBO2 as the solvent. The structure of SrLiCrTi4O11 was refined in the orthorhombic space group Pnma (Z = 4), while SrLiFeTi4O11 appeared to adopt a four-times larger orthorhombic unit cell with Pbcn (Z = 16). The structures can be described by a close-packed arrangement of Sr and O atoms. The unit cell contains six `compact planes' perpendicular to [100] in the layer sequence ABACBC [(chc)2]. Ti and Cr or Fe atoms occupy some of the interstitial octahedral sites created, whereas Li atoms are in tetrahedral sites. Depending on the synthesis conditions of SrLiCrTi4O11, the distribution of Cr and Ti atoms on the four possible crystallographic sites is not the same. Having a similar compact-planes sequence, SrLiCrTi4O11 and SrLiFeTi4O11 structures differ in the arrangement of Sr and O atoms per layer of close packing, which also induces a correlated variation in the Li-tetrahedra distribution.

International audience; LiTiOAs1−xPxO4 (0 ≤ x ≤ 1) compounds have been prepared using solutions of Li, Ti, As and P elements as starting products. Selected compositions have been investigated by powder X-ray or neutrons diffraction analysis, Raman and infrared spectroscopy. The structure of LiTiOAs1−xPxO4 (x=0, 0.5 and 1) samples determined by Rietveld analysis is orthorhombic with Pnma space group. It is formed by a 3D network of TiO6 octahedra and XO4 (X=As1−xPx) tetrahedra where octahedral cavities are occupied by lithium atoms. TiO6 octahedra are linked together by corners and form infinite chains along a-axis. Ti atoms are displaced from the centre of octahedral units in alternating short (1.700–1.709 Å) and long (2.301–2.275 Å) Ti–O bonds. Raman and infrared studies confirm the existence of Ti–O–Ti chains. Thermal stability of LiTiOAsO4 has been reported.

The phase transition occurring at Tt = 528 K in the natural mineral and synthetic laser host compound KPb2Cl5 has been characterized by means of both single-crystal X-ray diffraction (XRD) as a function of temperature and differential scanning calorimetry (DSC). The K+ and Pb2+(2) cations order on passing from the high-temperature orthorhombic phase (space group Pmcn; a = 8.951, b = 8.015, c = 12.683 A, Z = 4 at 623 K) to the low-temperature monoclinic one (space group P21/c; a = 8.849, b = 7.918, c = 12.472 A, = 90.11°, Z = 4, at room temperature), leading to a group-subgroup first-order phase transition displaying moderately fast kinetics and low entropy production upon thermal cycling around Tt. The positional entropy calculated from our crystal structure models corresponds to the transition entropy measured by DSC within the experimental error, and amounts to about 0.34 R. The driving force for the phase transition, A 22 J mol-1, remains negligible with respect to both the thermal energy at Tt (RTt 4.4 kJ mol-1) and the transition latent heat (H 790 J mol-1), thereby suggesting that this phase transition is a close-to-equilibrium process.

Li0.5M0.25TiOAsO4 (M=Mg,Co,Ni,Zn) oxyarsenates powders were prepared by coprecipitation method from dilute solution of Li2CO3,M(NO3)2×H2O (M=Mg,Co,Ni,Zn), (NH4)H2AsO4 and TiCl4 in ethanol. The resulting powders, obtained after drying at about 60 °C, were heated progressively with intermittent grindings at 200 °C–750 °C in air. These new compounds crystallize in the monoclinic system with space group P21∕c. Their parameters are functions of M2+ ion size.

International audience; Centimeter-sized single crystals of pure and Er-doped KPb2Cl5 were successfully grown by the Bridgman–Stockbarger method using silica ampoules sealed under HCl gas...

A new iron titanyl oxyphosphate Fe0.50TiO(PO4) was synthesized by both solid-state reaction and Cu2+–Fe2+ ion exchange method. The material was then characterized by X-ray diffraction, Mossbauer spectroscopy, magnetic susceptibility measurements and Raman spectroscopy. The crystal structure of the compound was refined, using X-ray powder diffraction data, by Rietveld profile method; it crytallizes in the monoclinic system, space group P21/c (No.14), with a = 7.4039 ( 3 ) A , b = 7.3838 ( 3 ) A , c = 7.4083 ( 3 ) A , β = 120.36 ° ( 1 ) , V = 349.44 ( 2 ) A 3 and Z = 4 . The volume of the title compound is comparable to those of the M0.50IITiO(PO4) series, where MII=Mg, Co, Ni and Zn. The framework is built up from [TiO6] octahedra and [PO4] tetrahedra. [TiO6] octahedra are linked together by corners and form infinite chains along the c-axis. Ti atoms are displaced from the center of octahedral units showing an alternating short distance (1.73 A) and a long one (2.22 A). These chains are linked together by [PO4] tetrahedra. Fe2+ cations occupy a triangle-based antiprism sharing two faces with two [TiO6] octahedra. Mossbauer and magnetic measurements show the existence of iron only in divalent state, located exclusively in octahedral sites with high spin configuration (t2g4eg2). Raman study confirms the existence of Ti–O–Ti chains.

International audience; The luminescence properties of Yb3+-doped Li6Y(BO3)3 crystalline material are presented for applications as active medium in diode pumped (short pulse) lasers emitting around 1040 nm and pumped at 975 nm. A single crystal of several centimeter size was grown by the Czochralski method. The absorption and emission spectra were recorded. This borate exhibits a strong absorption line around 975 nm and a broad emission line around 1040 nm. The fluorescence lifetime associated to this intense 2F5/2 → 2F7/2 transition is about 1.1 ms. All these parameters make this material a good host for short pulse laser applications. First laser tests have been performed by diode-pumping in a plano-concave cavity.

The new vanadate BiMgVO5 has been prepared and its structure has been determined by single crystal X-ray diffraction: space group P 2 1 / n , a = 7.542 ( 6 ) A , b = 11.615 ( 5 ) A , c = 5.305 ( 3 ) A , β = 107.38 ( 5 ) ° , w R 2 = 0.0447 , R = 0.0255 . The structure consists of [Mg2O10] and [Bi2O10] dimers sharing their corners with [VO4] tetrahedra. The ranges of bond lengths are 2.129–2.814 A for Bi–O; 2.035–2.167 A for Mg–O and 1.684–1.745 A for V–O. V–O bond lengths determined from Raman band wavenumbers are between 1.679 and 1.747 A. An emission band overlapping the entire visible region with a maximum around 650 nm is observed.

International audience; The luminescence characteristics of Eu3+ in the borates Li6Y(BO3)3 and Li3La2(BO3)3 and the recently discovered oxyborates LiLa2O2BO3, LiLn6O5(BO3)3 (Ln=Y,Gd) and Li2Lu5O4(BO3)3 have been investigated and compared to those in the borates LnBO3 (Ln=La,Y) and the oxyborates “Ln3BO6” (Ln=La,Gd). The probability of electric dipole f–f transitions is generally markedly higher in oxyborates than in borates. This is ascribed to the highly anisotropic environment of rare earth ions and the low position of the charge transfer states. Consequently, the Eu3+-activated oxyborates are characterized by a deeper red emission and faster decay. The luminescence characteristics of Eu3+ in the borates Li6Y(BO3)3 and Li3La2(BO3)3 and the recently discovered oxyborates LiLa2O2BO3, LiLn6O5(BO3)3 (Ln=Y,Gd) and Li2Lu5O4(BO3)3 have been investigated and compared to those in the borates LnBO3 (Ln=La,Y) and the oxyborates “Ln3BO6” (Ln=La,Gd). The probability of electric dipole f–f transitions is generally markedly higher in oxyborates than in borates. This is ascribed to the highly anisotropic environment of rare earth ions and the low position of the charge transfer states. Consequently, the Eu3+-activated oxyborates are characterized by a deeper red emission and faster decay.

International audience; Experimental observations on spiralgrowth phenomena in the Cz-growth of Li6Gd(BO3)3 single crystals are described. With careful observations at the meniscus part during the pulling, we found that the faceting formation is closely correlated with a "dog-leg" footing in combination with unsteady melt convection modes. It is assumed that one of predominant origin of the so-called spiralgrowth should be the faceting inclined against the pulling axis at the meniscus part of the solid-liquid interface. Several origins reported so far are also discussed.

International audience; The investigation of the ternary phase diagram for BaOZrO2B2O3 has allowed single crystals to be grown by the flux method with formula BaZr(BO3)2. As this composition has been already announced in the literature, but without any structural data, the structure of BaZr(BO3)2 has been solved using X-ray data collected on a Kappa CCD diffractometer. This borate crystallizes in the trigonal symmetry with non-centrosymmetric space group R3c (no. 161): a=b=5.167(1) Å and c=33.913(7) Å; Z=6. The structure derived from the dolomite-type with a doubling of the c parameter. Along the c-axis, alternated layers of Ba atoms and Zr atoms are separated by planes of BO3 groups. BaO6 and ZrO6 octahedra so formed are linked by their corners and each Ba(Zr) octahedron is linked to six Zr(Ba) octahedra and to six borate groups. The small deviation from centrosymmetry is attested by considering refinement agreement for the (weak) reflections (h k l) with odd value of l, and positive response of the powder second harmonic generation (SHG) test. A new J.C.P.D.S.-I.C.D.D. card is proposed for this compound.

A new oxyborate with a composition corresponding to the formula Na3La9O3(BO3)8 has been discovered in the ternary oxide system Na2OLa2O3B2O3. Single crystals of this compound have been grown by spontaneous crystallization from melts of the constituent binary oxides during slow cooling. The structure of Na3La9O3(BO3)8 has been solved using X-ray data collected on a Nonius Kappa CCD diffractometer (Mo Kα radiation). The unit cell is hexagonal (space group P-62m, Z=1) with a=8.9033(3), c=8.7131(3) A and V=598.14 A3. Refinement of 49 parameters using 684 independent reflections with an intensity I>2σ(I) (Friedel not merged for absolute structure determination) results in R1=0.015 (wR2=0.030). The structure is characterized by alternate stacking along the c-axis of NaBO, BO, La and LaO containing layers with a mirror plane at z=1/2. A framework of La9O3 rings and rows of BO3 triangles running along the c-direction is established. Each La9O3 ring is constituted of three La4O tetrahedra sharing a common La corner. The presence in the structure of oxygen atoms surrounded by lanthanum atoms only justifies the oxyborate label of the new compound.

The structure of the oxyphosphate Li0.50Ni0.25TiO(PO4) has been determined from conventional X-ray and neutron powder diffraction data. The parameters of the monoclinic cell (space group P21/c, Z=4), obtained from X-ray results, are: a=6.3954(6) Å, b=7.2599(6) Å, c=7.3700(5) Å, and β=90.266(6)°; those resulting from neutron study are: a=6.3906(7) Å, b=7.2568(7) Å, c=7.3673(9) Å, and β=90.234(7)°. Refinement by the Rietveld method using whole profile, leads to satisfactory reliability factors: cRwp=0.128, cRp=0.100, and RB=0.038 for X-ray and cRwp=0.110, cRp=0.120, and RB=0.060 for neutrons. The structure of Li0.50Ni0.25TiO(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 tetrahedra. In this framework, there are octahedral cavities occupied by Li and Ni atoms: Li occupies the totality of the 2a sites and Ni occupies statistically half of the 2b sites. Ti atoms are displaced from the center of octahedra units in alternating long (2.242 Å) and short (1.711 Å) Ti–O bonds along chains.

We describe the luminescence and scintillation of indium disilicate (In 2 Si 2 O 7 ), an inorganic scintillator containing a large amount of 115 In. The maximum fluorescence occurs in the near UV range at 335 nm with a complicated decay including a fast component of less than 100 ns and a long one of more than a microsecond. Room temperature emission intensity was quite weak while the quantum efficiency became reasonably good at cryogenic temperature. Scintillation was measured using α-particles of 6.09 MeV and 8.785 MeV from 300 to 4 K. A maximum of intensity is observed at 50 K. A fast component (τ ⋍ 20 ns) with a constant intensity superimposes to a slow one of which the intensity has a maximum at 50 K and for which the decay constant rises as the temperature decreases.

Un dispositif de croissance cristalline basé sur la technique de l'échangeur thermique a été développé au laboratoire. Cette méthode a été appliquée à l'obtention de céramiques orientées de YBa2Cu3O7-x. Les conditions expérimentales ainsi que les différents paramètres thermiques afférents à la méthode de texturation utilisée sont précisés. La texturation des échantillons obtenus a été caractérisée par diffraction des rayons X, par microscopie optique et par microscopie électronique à balayage ; la susceptibilité alternative a révélé une transition supraconductrice à 92 K et une densité de courant critique de 5 000 A/cm2 à 77 K et sans champ magnétique.

The superconducting properties of Tl- and Bi- based high Tc oxide crystals are discussed in relation to YBCO and to artificial, low Tc, layer and multifilamentary structures. New data from magnetisation studies of a Tl:2212 crystal, and also of multifilamentary NbTi samples are presented and interpreted together with relevant literature data in terms of an H - T phase diagram for the Bi and Tl oxides which includes a three-dimensional ’vitreous’ region at low temperatures, an intermediate two-dimensional region and a higher-temperature three-dimensional region. A high-T, 3-D region occurs in all bulk superconductors when the penetration depth and coherence length become longer than the superlattice spacing, but in Bi and Tl cuprates only close to Tc. To understand the other regions we start with the supposition that the materials consist of Josephson-coupled superconducting CuO layers. The Lawrence- Doniach model is to be developed by incorporating recent ideas of Deutscher and Kapitulnik, Kes et al, and others. We furthermore make the working hypothesis that the CuO layers are separated by normalconducting layers in which superconductivity can be induced by the proximity effect. The crossover or possible phase transition between the low-T, 3-D region and the intermediate 2-D region then occurs when the applied field is sufficient to critically weaken the induced superconductivity. These ideas are discussed in relation to the intrinsic flux-pinning effect of layer structures, and the best strategy of using both intrinsic and extrinsic pinning to optimise critical transport current density. Radiation treatments, and in particular low-temperature electron irradiation are discussed as means of adding controlled extrinsic pinning.

The irreversibility line H*(T) of a Tl2Ba2CaCu2O8 single crystal varies as {ie1147-1} and diverges below 20 K. These phenomena could be related to a breakdown field of a weak superconductivity induced in BaO-TlO-TIO-BaO layer blocks by superconducting CuO layer blocks. The magnetization at the transition can be calculated assuming the existence of a second order phase transition.

International audience; A single crystal Pb2.07K0.56Nb0.91Ta4.15O15 has been grown by the flux method. It crystallizes with the tetragonal tungsten bronze structure. Two transitions have been determined by dielectric, pyroelectric and birefringence measurements: ferroelastic-ferroelectric phase →371 K ferroelastic-paraelectric phase →658 K paraelastic-paraelectric phase. Spontaneous polarization and spontaneous strain are respectively equal to 29 μC · cm-2 and 8 × 10-4 at room temperature. Polar axis is along the [010] direction. Electrical switching of the ferroelastic domains at room temperature shows clearly the existence of a ferroelastic-ferroelectric coupling.

CsCdBr 3 : Nd 3+ crystals have been studied by laser selective excitation and time resolved spectroscopy. Due to the charge compensation resulting from the Nd 3+ /Cd 2+ substitution, the proportion of Nd 3+ pairs is very large and does not follow the statistical laws. This proportion has been measured, its variation with concentration has been established and the effect of codoping with a monovalent metal observed. From a comparison between the properties of single ions and pairs, energy transfers have been analysed. De-excitation channels have been determined for some excited levels from the dynamics and the relative intensities of luminescence lines. An unusual behaviour, which can lead to applications, has been observed: the 4 F 3/2 luminescence of pairs if favoured with respect to that of single ions. This behaviour is well explained Etude experimentale par des techniques d'excitation selective par laser pulse avec resolution temporelle, avec une grande proportion de Nd 3+ associes en paires, en suivant par les lois de la statistique, du fait de la substitution de Cd 2+ par Nd 3+ . Mesure de cette proportion et de sa variation avec la concentration; observation d'un effet de codopage par un ion monovalent. Analyse des transferts d'energie. Determination des chemins de desexcitation depuis quelques niveaux excites a partir de la dynamique et des intensites relatives des raies de luminescence. Observation de la luminescence du niveau 4 F 3/2 favorisee pour les paires par rapport aux ions isoles; interpretation

The growth of Ce1−xPrxO2 single crystals (x≃0.05) has been investigated in connection with a systematic research work o n rare earth based red pigments. Ce1−xPrxO2 crystals have been grown by spontaneous nucleation during slow cooling of a high temperature solution using PbF2-Pb3P2O8-NaF or Na2B4O7-NaF as solvents. X-ray diffraction, chemical analysis and optical study were performed on the obtained single crystals. Stabilization of Pr4+ in cerium oxide accounted for the observed red color.

The structure of potassium tantalum oxyfluoride K₂Ta₂O₃F₆ has been determined from a Patterson synthesis and refined by least squares (R = 0.065). The orthorhombic unit cell has the space group Pnma (a = 10.212 (5) Å ; b = 5.581 (3) Å ; c = 14.499 (7) Å) and contains four motifs. The structure is made up of double infinite zigzag chains along the [010] direction. These chains are formed by the (TaO₃F₃) ⁴⁻ octahedra sharing three oxygen corners of a common face. The K⁺ ions occupy the vacant sites between the files and ensure the cohesion of the lattice., La structure de l'oxyfluorotantalate de potassium K₂Ta₂O₃F₆ a été déterminée à partir d'une synthèse de Patterson et affinée par la méthode des moindres carrés (R = 0,065). La maille élémentaire de symétrie orthorhombique comporte le groupe spatial Pnma (a = 10,212 (5) Å ; b = 5,581 (3) Å ; c = 14,499 (7) Å) et contient quatre motifs formulaires. Le réseau est formé de chaînes doubles se développant en zigzag dans la direction de l'axe b, constituées d'octaèdres (TaO₃F₃) ⁴⁻ mettant en commun trois sommets oxygénés d'une même face. Des ions K⁺ occupent les sites vacants entre les files assurant la cohésion du réseau., Vlasse Marcus, Chaminade Jean-Pierre, Pouchard Michel. La structure cristalline de l'oxyfluorotantalate de potassium K2Ta2O3F6. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 99, 1, 1976. pp. 3-7.