Space Group Ia3d Research Articles

Influence of Nanosize Silica Particles on the Rheological Behaviour of Lyotropic Cubic Phase of Glucopone (APG) Surfactant

The effect of nanosize silica particle on the stability, structures and rheological behaviours of cubic liquid crystalline phases of Glucopone/water/heptane system were investigated. Small-angle X-ray scattering (SAXS) and polarizing microscope were used for phase identification and structure characterization. SAXS scattering profile was characteristic to cubic phase before and after the addition of silica particles. The cubic samples showed several diffraction peaks and can be assigned to the Ia3d space group. The area per surfactant molecule was found to increase as the silica concentrations was increased. Moreover, the rheological study on the cubic phase with different silica concentration was performed. The frequency-dependent storage and loss modulus were found to be characteristic of the cubic phase in the linear viscoelastic region. The cubic samples behave as solid-like material with storage modulus G’~ 0.7106 Pa typical of cubic lyotropic materials. The elasticity of cubic samples was found to increase with silica concentration. The increase in the elasticity was ascribed to the network and the formation of smaller structure as indicated by SAXS measurements. As temperature was further increased a decreased in the elasticity was observed confirming the structural change as indicated by the change in slopes of G’ and G”. The cubic samples exhibited shear thinning behaviours, with the dynamic viscosity being affected by the silica particles concentrations and the effect of silica particles on the rheological behaviours was quite noticeable as the concentration increased. The results showed strong correlation between rheology and microstructural changes in the dispersion of nanoparticle silica in the cubic phase system.

The reaction of Li6.5La3Zr1.5Ta0.5O12 with water

The Li-ion conductor “Li6.5La3Zr1.5Ta0.5O12” (LLZT) with garnet structure is prepared by solid-state reaction in an alumina crucible; its stability in water is investigated at room temperature. A Li+/H+ exchange is characterized by TGA, 7Li and 27Al MAS NMR, neutron diffraction, and TEM. In water, Li+/H+ exchange leads to a new garnet oxide “Li6.5−xHxLa3Zr1.5Ta0.5O12” (H-LLZT) with space group Ia–3d; the lattice parameter of H-LLZT is increased by the exchanged protons. Both LLZT and a grain boundary phase LiAlO2 are unstable in water. The exchanged protons in H-LLZT displace Li from the octahedral sites bridging the 24d tetrahedral sites; they form a strong OH bond that distorted the site. The amorphous phase LiAlO2 in the grain boundary dissolves on exposure to water, which inhibits Li-ion transport across the grain boundary.

Electrospinning preparation and photoluminescence properties of Y3Al5O12:Tb3+ nanostructures.

Novel nanostructures of Y3Al5O12:Tb(3+) (denoted as YAG:Tb(3+) for short) nanobelts and nanofibers were fabricated by calcination of the respective electrospun PVP/[Y(NO3)3 + Tb(NO3)3 + Al(NO3)3] composite nanobelts and nanofibers. YAG:Tb(3+) nanostructures are cubic in structure with a space group of Ia 3d. The thickness and width of the YAG:7%Tb(3+) nanobelts are respectively ca. 125 nm and 5.9 ± 0.3 m, and the diameter of YAG:7%Tb(3+) nanofibers is 166.0 ± 20 nm (95% confidence level). The YAG:Tb(3+) nanostructures emit predominantly at 544 nm from the energy levels transition of (5) D4 → (7) F5 of Tb(3+) ions under the excitation of 274-nm ultraviolet light. It was found that the optimum doping molar concentration of Tb(3+) ions for YAG:Tb(3+) nanostructures was 7%. Compared with YAG:7%Tb(3+) nanofibers, YAG:7%Tb(3+) nanobelts exhibit a stronger photoluminescence (PL) intensity under the same doping concentration. Commission International de l'Eclairage (CIE) analysis demonstrates that the emitting colors of YAG:Tb(3+) nanostructures are located in the green region and color-tuned luminescence can be obtained by changing the doping concentration of Tb(3+) and morphologies of the nanostructures, which could be applied in the field of optical telecommunication and optoelectronic devices. The possible formation mechanisms of YAG:Tb(3+) nanobelts and nanofibers are also proposed.

Evaluation of growth, thermal and spectroscopic properties of Yb^3+-doped GSGG crystals for use in ultrashort pulsed and tunable lasers

A series of high quality Yb3+-doped gadolinium scandium gallium garnet (Yb:GSGG) single crystals with different Yb3+ ion concentration (7.5, 10, 15 and 30 at.%) has been grown by means of optical floating zone (OFZ). Crystal structure was analyzed with X-ray powder diffraction (XRPD), showing that the Yb:GSGG crystal possesses a cubic structure with space group Ia3d, and the lattice constants decrease linearly as the Yb3+ concentration increases. Effective elemental segregation coefficients and chemical composition were investigated by X-ray fluorescence (XRF), suggesting that some Yb3+ ions occupy the octahedral site when the Yb3+ ion concentration is higher than 10 at.%. The thermal properties of Yb:GSGG crystals were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficients. Thermal conductivity was then calculated, and it exhibits a tendency to decrease with increasing Yb3+ ion concentration. Spectroscopic characterization of Yb:GSGG crystals was performed at room temperature (RT), and the stimulated emission cross section was calculated using the reciprocity method (RM) and the Fuchtbauer−Ladenburg (F−L) formula, respectively. In comparison with the radiative lifetime of the 2F5/2→2F7/2 transition, the effect of radiation trapping on the fluorescence lifetime is discussed. These research results indicate that Yb:GSGG can be regarded as a promising candidate for use in an ultrashort pulsed and tunable laser.

Structure and H position of tetragonal hydrogarnet derived from CaGeO3garnet

Hydrogarnets, represented by hydrogrossular, are produced by the replacement of (ZO4)4- in garnets by (H4O4)4- (Z: tetrahedral cation) and the vacancies of tetrahedral cations are created by this replacement. Most of reported hydrogarnets crystallizes with cubic symmetry (space group Ia-3d). To our knowledge, Ca3Mn2[SiO4]2.07[H4O4]0.93 with space group I41/acd (tetragonal) [1] has been only reported as a low-symmetry hydrogarnet. In the cubic hydrogarnets, all O atoms are crystallographically equivalent, whereas in low-symmetric one, they can be located at non-equivalent sites. Therefore, the investigation of low-symmetry hydrogarnes is important to gain knowledge of the site preference of H atoms. Recently, we have successfully synthesized the single crystal of a new low-symmetry hydrogarnet CaGe0.924O3H0.304 (= Ca3(CaGe)[GeO4]2.696[H4O4]0.304) with tetragonal space group I41/a, at 3 GPa and 1273 K under the presence of H2O component. This tetragonal hydrogarnet is produced by the partial replacement of (GeO4)4- in high-pressure CaGeO3 garnet, Ca3(CaGe)[GeO4]3, by (H4O4)4-. In the present study, we report the single crystal X-ray diffraction study of this hydrogarnet at 98 and 298 K. In the structure refinement at 298 K, the occupancy parameters resulted in 0.393(2) for tetrahedral Z2(Ge) site, coordinated only by O6 atoms, and showed no significant deviation from 1.0 for the remaining cation sites. The bond valence sums of each atom except O6 atom agree with the valences of occupied atoms, whereas that of O6 atom are 1.50, deviating largely from oxygen valence. Thus, the substitution of OH groups for O atoms in the present sample occurs only at O6 site, which indicates that O6 is the most preferential site for the OH substitution. The position of H atom will be examined from the residual electron density distributions at a low temperature of 98 K, and the hydrogen bonding in the crystal structure will be discussed.

Effect of V-doping on the structure and conductivity of garnet-type Li5La3Nb2O12

The effect of isovalent V substitution for Nb in Li5La3Nb2O12 on the electrical conductivity properties of the garnet-type structure was investigated by various physical methods, including powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and 7Li nuclear magnetic resonance (NMR) spectroscopy. Garnet-type metal oxides of the nominal chemical formula, Li5La3Nb2−xVxO12 (x = 0 – 0.25) were prepared by conventional solid-state method at elevated temperature in air. PXRD results showed that the cubic garnet-type structure with space group (s.g.) of Ia-3d was maintained, but several peaks attributed to secondary phase LaVO4 (s.g.P21/n) were also observed. SEM measurements indicate doping V for Nb improved particle-to-particle contact. The effect of V substitution for Nb in Li5La3Nb2O12 on ionic conductivity was also studied by AC impedance spectroscopy. The total (bulk + grain boundary) conductivity gradually increased with V content up until x = 0.15 and decreased thereafter. The x = 0.15 showed the highest total conductivity of 6 × 10−6 S cm−1 at room temperature, with the lowest activation energy of 0.37 eV.

Er∶YbGG纳米粉体制备及荧光发光性能研究

Er:YbGG nanopowder was prepared by sol-gel method. XRD, TG-DTA, SEM and spectra analysis were utilized to investigate the phase structure and spectrum properties of the powder. The experiment results indicate that the fine Er:YbGG nanopowder belongs to a cubic phase with a space group of Ia-3d and lattice parameter a=1.2162 nm. Under 980 nm excitation, an intensive fluorescence emission peak appears near 1533 nm in the emission spetrum of Er:YbGG nanopowder, and the high intensity of the emission is attributed to the energy transmission between Yb3+ and Er3+ ions.

A Simple Microfluidic Chip Design for Fundamental Bioseparation

A microchip pressure-driven liquid chromatographic system with a packed column has been designed and fabricated by using poly(dimethylsiloxane) (PDMS). The liquid chromatographic column was packed with mesoporous silica beads of Ia3d space group. Separation of dyes and biopolymers was carried out to verify the performance of the chip. A mixture of dyes (fluorescein and rhodamine B) and a biopolymer mixture (10 kDa Dextran and 66 kDa BSA) were separated and the fluorescence technique was employed to detect the movement of the molecules. Fluorescein molecule was a nonretained species and rhodamine B was attached onto silica surface when dye mixture in deionized water was injected into the microchannel. The retention times for dextran molecule and BSA molecule in biopolymer separation experiment were 45 s and 120 s, respectively. Retention factor was estimated to be 3.3 for dextran and 10.4 for BSA. The selectivity was 3.2 and resolution was 10.7. Good separation of dyes and biopolymers was achieved and the chip design was verified.

Evidence of Basic Medium in the Polar Nanochannels of the Inverse Bicontinuous Cubic Phase of a Guerbet Glycolipid: A Steady-State and Time-Resolved Fluorescence Study

Characteristic structures and properties of nanochannels are thought to play important roles in biological activity and chemical and physical processes at the interfaces. In this work, we characterized the polar nanochannels of the inverse bicontinuous cubic phase of the 2-hexyl-decyl-β-d-glucopyranoside/water system, which has a gyroid Ia3d space group symmetry, by introducing fluorescent probes. The fluorescence signals of tryptophan (Trp) and two of its ester derivatives (Trp-C4 and Trp-C8) show a local basic environment inside the nanochannels that is equivalent to an aqueous solution of pH ≥ 10.0. This was confirmed by measuring the fluorescence spectra of aqueous tryptophan in different pH solutions. The basic effect is attributed to the restricted motion of water in the nanochannels (diameter of 2.3 nm) in which water molecules are situated very close to the OH groups of the sugar units. The very small channels also force the tryptophan moiety to be very close to the sugar units and the water molecules in which the local environment is mostly basic. We characterized the hydrophobic region of the lipid by measuring the fluorescence change of pyrene upon incorporation in the tail region. A larger hydrophobicity was reflected in the measured small ratio of the vibronic peak intensities of pyrene (I1/I3). This is attributed to the compact interaction of the double alkyl chains of the lipid with the pyrene molecules. When adding Trp-C8 to the lipid assembly, there was no change in the I1/I3 ratio nor in the pyrene lifetimes which implies that there is no interaction between the pyrene and the C8-chain. This observation indicates that the pyrene molecules are well-shielded inside the tail region. The measured two lifetime components for each tryptophan and pyrene point to the presence of a degree of heterogeneity and flexibility in the lipid self-assembly. These properties are crucial for carrying out different biological functions such as the ability to accommodate various molecular sizes. The current results suggest the structural importance of very narrow polar nanochannels of the lipidic cubic phase which may facilitate the transfer of highly polar substances, such as ions, to the cells.

Facile Electrospinning Preparation and Up-Conversion Luminescence Performance of Y3Al5O12:Er3+, Yb3+ Nanobelts

Electrospinning technique was used to prepare \( {\text{PVP}}/\left[ {{\text{Y}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} + {\text{Yb}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} + {\text{Er}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} + {\text{Al}}\left( {{\text{NO}}_{ 3} } \right)_{ 3} } \right] \) composite nanobelts and novel structures of Y3Al5O12:Er3+, Yb3+ (denoted as YAG:Er3+, Yb3+ for short) nanobelts have been successfully fabricated after calcination of the relevant composite nanobelts at 900 °C for 8 h. YAG:Er3+, Yb3+ nanobelts were characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and fluorescence spectroscopy. XRD analysis indicated that YAG:Er3+, Yb3+ nanobelts were cubic in structure with space group Ia3d. SEM analysis and histograms revealed that the width of YAG:Er3+, Yb3+ nanobelts was ca. 1.8 ± 0.37 μm under the 95 % confidence level, and the thickness was ca. 81.8 nm. Up-conversion emission spectra analysis manifested that YAG:Er3+, Yb3+ nanobelts respectively emitted strong green and red emissions centering at 522, 554 and 648 nm under the excitation of a 980-nm diode laser. The green emissions were assigned to the energy levels transitions of \( ^{ 2} {\text{H}}_{ 1 1/ 2} ,^{ 4} {\text{S}}_{ 3/ 2} \to^{ 4} {\text{I}}_{ 1 5/ 2} \) of Er3+ ions, and the red emission originated from the energy levels transition of \( ^{ 4} {\text{F}}_{ 9/ 2} \to ^{ 4} {\text{I}}_{{{\text{l5}}/ 2}} \) of Er3+ ions. The up-conversion luminescence of YAG:Er3+, Yb3+ nanobelts doped with various concentrations of Yb3+ and Er3+ was studied and the optimum molar ratio of Yb3+ to Er3+ was found to be 15:1. CIE analysis demonstrated that color-tuned luminescence can be obtained by adjusting doping concentrations of Yb3+ and Er3+ ions, which could be applied in the fields of optical telecommunication and optoelectronic devices. The up-conversion luminescent mechanism and the formation mechanism of YAG:Er3+, Yb3+ nanobelts were also proposed.

Thermal, spectroscopic and laser properties of Nd3+ in gadolinium scandium gallium garnet crystal produced by optical floating zone method

A neodymium-doped gadolinium scandium gallium garnet (Nd:GSGG) single crystal with dimensions of Φ 5×20mm2 has been grown by means of optical floating zone (OFZ). X-ray powder diffraction (XRPD) result shows that the as-grown Nd:GSGG crystal possesses a cubic structure with space group Ia3d and a cell parameter of a=1.2561nm. Effective elemental segregation coefficients of the Nd:GSGG as-grown crystal were calculated by using X-ray fluorescence (XRF). The thermal properties of the Nd:GSGG crystal were systematically studied by measuring the specific heat, thermal expansion and thermal diffusion coefficient, and the thermal conductivity of this crystal was calculated. The absorption and luminescence spectra of Nd:GSGG were measured at room temperature (RT). By using the Judd–Ofelt (J–O) theory, the theoretical radiative lifetime was calculated and compared with the experimental result. Continuous wave (CW) laser performance was achieved with the Nd:GSGG at the wavelength of 1062nm when it was pumped by a laser diode (LD). A maximum output power of 0.792W at 1062nm was obtained with a slope efficiency of 11.89% under a pump power of 7.36W, and an optical–optical conversion efficiency of 11.72%.

Spectroscopic properties of Nd3+:Lu3ScAl4O12 single crystal

Nd:Lu3ScAl4O12 single crystal has been grown by the Czochralski method. The segregation coefficient of Nd3+ ions in LuSAG crystal is 0.22. X-ray powder diffraction (XRD) experiments show that the Nd:LuSAG crystal crystallizes in cubic structure with space group Ia3d and its cell parameters are a = 1.1953 nm. The absorption and fluorescence spectra of Nd:LuSAG crystal were investigated at room temperature. The spectral parameters were calculated based on Judd–Ofelt (J–O) theory, and the intensity parameters Ω2, Ω4 and Ω6 were obtained to be 0.14, 3.38, and 4.88 × 10−20 cm2, respectively. The calculated spontaneous radiative probabilities, branching ratios, radiative lifetime and quantum efficiency have been evaluated for the 4F3/2 excited state using the calculated intensity parameters. The results indicate that this crystal can be considered as a promising material for solid-state laser application.

Facile Electrospinning Preparation of Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub> Nanobelts

PVP/[Y(NO3)3+Al (NO3)3] composite nanobelts were fabricated via electrospinning combined with sol-gel process and novel structure of Y3Al5O12(denoted as YAG for short) nanobelts have been obtained after calcination of the relevant composite nanobelts. The structural properties were characterized by X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XRD analysis indicated that the composite nanobelts were amorphous, and YAG nanobelts were cubic in structure with space group Ia3d. FTIR analysis manifested that pure YAG nanobelts were formed at 900oC. SEM analysis and histograms revealed that the width of the composite nanobelts and YAG nanobelts were 3.5 μm and 2.4 μm, and the thickness were 240 nm and 112 nm, respectively, under the 95% confidence level. The formation mechanism of YAG nanobelts was discussed in detail.

Structural characterization of lyotropic liquid crystals containing a dendrimer for solubilization and release of gallic acid

The role of 2nd generation polypropyleneimine (PPIG2) dendrimer in controlling the release of gallic acid (GA) as a model drug from lyotropic liquid crystal was explored. GA (0.2wt%) was solubilized in three types of mesophases: lamellar (Lα), cubic (space group of Ia3d, QG), and reverse hexagonal (HII), composed of GMO and water (and d-α-tocopherol, or tricaprylin in the case of HII mesophases).Small angle X-ray scattering (SAXS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) along with UV spectrophotometry were utilized to elucidate the structure modifications and release resulting from the cosolubilization of GA and PPIG2.Solubilization of PPIG2 into Lα and QG phases caused transformation of both structures to HII. The diffusion of GA out of the mesophases was found to be dependent on water content and PPIG2 concentration. Rapid release from Lα+PPIG2 and QG+PPIG2 mesophases was recorded. The release from both HII mixtures (with d-α-tocopherol and tricaprylin) was shown to be dependent on the type of oil.Release studies conducted for 72h showed that GA release can be modulated and sustained by the presence of PPIG2, supposedly due to the electrostatic interactions between the dendrimer and the drug molecule.

Synthesis and Crystal Chemistry of the Fast Li-Ion Conductor Li7La3Zr2O12 Doped with Fe

Nominal Li7La3Zr2O12 (LLZO) garnet, doped with (57)Fe2O3, was synthesized by sintering oxides and carbonates at T = 1100 °C in air. X-ray powder diffraction measurements show that Li(7-3x)Fe(3+)(x)La3Zr2O12 with x = 0.19 crystallizes in the cubic space group Ia-3d, with a0 = 12.986(4) Å at room temperature. SEM and electron microprobe measurements were made to obtain compositional information and check for the presence of phases other than garnet. Inductively coupled plasma optical emission spectroscopy measurements were made to determine the Li content. (57)Fe Mössbauer spectra obtained at 295 and 80 K show that about 96% of the total iron occurs as Fe(3+) and 4% as Fe(2+). Roughly two-thirds of the Fe(3+) cations are assigned to the tetrahedral site (24d) and roughly one-quarter to a highly distorted site (possibly at 96h) in the garnet structure. Smaller amounts of Fe(3+) and Fe(2+), around 5% each, occur at other crystallographic sites. On the basis of published (27)Al MAS NMR results and analysis of the (57)Fe Mössbauer spectra, it appears that at low concentrations Al(3+) and Fe(3+) substitute in Li7La3Zr2O12 in a similar manner. The aliovalent substitution Al(3+)/Fe(3+) ↔ 3Li(+) in LLZO stabilizes the cubic phase and also probably promotes its high Li-ion conductivity.

Nomenclature of the garnet supergroup

The garnet supergroup includes all minerals isostructural with garnet regardless of what elements occupy the four atomic sites, i.e., the supergroup includes several chemical classes. There are presently 32 approved species, with an additional 5 possible species needing further study to be approved. The general formula for the garnet supergroup minerals is {X3}[Y2](Z3)ϕ12, where X, Y, and Z refer to dodecahedral, octahedral, and tetrahedral sites, respectively, and ϕ is O, OH, or F. Most garnets are cubic, space group Ia3d (no. 230), but two OH-bearing species (henritermierite and holtstamite) have tetragonal symmetry, space group, I41/acd (no. 142), and their X, Z, and ϕ sites are split into more symmetrically unique atomic positions. Total charge at the Z site and symmetry are criteria for distinguishing groups, whereas the dominant-constituent and dominant-valency rules are critical in identifying species. Twenty-nine species belong to one of five groups: the tetragonal henritermierite group and the isometric bitikleite, schorlomite, garnet, and berzeliite groups with a total charge at Z of 8 (silicate), 9 (oxide), 10 (silicate), 12 (silicate), and 15 (vanadate, arsenate), respectively. Three species are single representatives of potential groups in which Z is vacant or occupied by monovalent (halide, hydroxide) or divalent cations (oxide). We recommend that suffixes (other than Levinson modifiers) not be used in naming minerals in the garnet supergroup. Existing names with suffixes have been replaced with new root names where necessary: bitikleite-(SnAl) to bitikleite, bitikleite-(SnFe) to dzhuluite, bitikleite-(ZrFe) to usturite, and elbrusite-(Zr) to elbrusite. The name hibschite has been discredited in favor of grossular as Si is the dominant cation at the Z site. Twenty-one end-members have been reported as subordinate components in minerals of the garnet supergroup of which six have been reported in amounts up to 20 mol% or more, and, thus, there is potential for more species to be discovered in the garnet supergroup. The nomenclature outlined in this report has been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (Voting Proposal 11-D).

Concerted Migration Mechanism in the Li Ion Dynamics of Garnet-Type Li7La3Zr2O12

The garnet-type Li7La3Zr2O12 (LLZO) belonging to cubic symmetry (space group Ia3̅d) is considered as one of the most promising solid electrolyte materials for all-solid state lithium ion batteries. In this study, the diffusion coefficient and site occupancy of Li ions within the 3D network structure of the cubic LLZO framework have been investigated using ab initio molecular dynamics calculations. The bulk conductivity at 300 K is estimated to be about 1.06 × 10–4 S cm–1 with an energy barrier of 0.331 eV, in reasonable agreement with experimental results. The complex mechanism for self-diffusion of Li ions can be viewed as a concerted migration governed by two crucial features: (i) the restriction imposed for occupied site-to-site interatomic separation, and (ii) the unstable residence of Li ion at the 24d site, which can serve as the trigger for ion mobility and reconfiguration of surrounding Li neighbors to accommodate the initiated movement. Evidence for Li ordering is also found at low temperature for the LLZO system.

Magnetic and magnetodielectric properties of erbium iron garnet ceramic

An Er3Fe5O12 ceramic has been sintered in oxygen atmosphere at 1400 °C for dielectric measurements. Its structural quality at room temperature has been checked by combining transmission electron microscopy and X-ray diffraction. It crystallizes in the cubic space group Ia3d with a = 12.3488(1). The dielectric permittivity (ε′) and losses (tan δ) measurements as a function of temperature reveal the existence of two anomalies, a broad one between 110 K and 80 K, attributed to the Er3+ spin reorientation, and a second sharper feature at about 45 K associated to the appearance of irreversibility on the magnetic susceptibility curves. In contrast to the lack of magnetic field impact on ε′ for the former anomaly, a complex magnetic field effect has been evidenced below 45 K. The isothermal ε′(H) curves show the existence of positive magnetodielectric effect, reaching a maximum of 0.14% at 3 T and 10 K. Its magnitude decreases as H is further increased. Interestingly, for the lowest H values, a linear regime in the ε′(H) curve is observed. From this experimental study, it is concluded that the ε′ anomaly, starting above the compensation temperature Tc (75 K) and driven by the internal magnetic field, is not sensitive to an applied external magnetic field. Thus, below 45 K, it is the magnetic structure which is responsible for the coupling between spin and charge in this iron garnet.

Luminescent properties of red-emitting LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor for white-LEDs

An Eu2+-activated oxynitride LiSr(4−y)B3O(9−3x/2)Nx:yEu2+ red-emitting phosphor was synthesized by solid-state reactions. The synthesized phosphor crystallized in a cubic system with space group Ia–3d. The LiSr4B3O(9−3x/2)Nx:Eu2+ phosphors exhibited a broad red emission band with a peak at 610nm and a full width at half maximum of 106nm under 410nm excitation, which is ascribed to the 4f65d1→4f7 transition of Eu2+. The optimal doped nitrogen concentration was observed to be x=0.75. The average decay times of two different emission centers were estimated to be 568 and 489ns in the LiSr3.99B3O8.25N0.5:0.01Eu2+ phosphors, respectively. Concentration quenching of Eu2+ ions occurred at y=0.07, and the critical distance was determined as 17.86Å. The non-radiative transitions via dipole–dipole interactions resulted in the concentration quenching of Eu2+-site emission centers in the LiSr4B3O9 host. These results indicate LiSr4B3O(9−3x/2)Nx:Eu2+ phosphor is promising for application in white near-UV LEDs.

Ionic distribution and conductivity in lithium garnet Li7La3Zr2O12

The garnet-related oxide with nominal formula Li7La3Zr2O12 prepared by the sol–gel method is cubic, space group Ia-3d with lattice parameter a=12.9720Å at room temperature. The occupancies of three lithium positions (24d, 48g, 96h) and the position of a small amount of Al3+ (ca 0.61wt%) inside the grains were determined by neutron diffraction. The occupancy of the 24d Li sites was reduced to 36.0% by the Al3+ occupying the 48g sites. The bulk and total Li+-ion conductivity at 25°C was 3.1×10−4Scm−1 and 1.4×10−4Scm−1 with an activation energy 0.34eV in the temperature range 25–160°C.