Preferential growth orientation of laser-patterned LiNbO3 crystals in lithium niobium silicate glass

Dots and lines consisting of LiNbO₃ crystals are patterned on the surface of 1CuO-40Li₂O-32Nb₂O₅-28SiO₂ (mole ratio) glass by irradiations of continuous-wave Nd:YAG laser (wavelength: λ=1064 nm), diode laser (λ=795 nm), and Yb:YVO₄ fiber laser (λ=1080 nm), and the feature of laser-patterned LiNbO₃ crystal growth is examined from linearly polarized micro-Raman scattering spectrum measurements. LiNbO₃ crystals with the c-axis orientation are formed at the edge parts of the surface and cross-section of dots. The growth direction of an LiNbO₃ along the laser scanning direction is the c-axis. It is proposed that the profile of the temperature distribution in the laser-irradiated region and its change along laser scanning would be one of the most important conditions for the patterning of crystals with a preferential growth orientation. Laser irradiation giving a narrow width is also proposed to be one of the important factors for the patterning of LiNbO₃ crystal lines with homogeneous surface morphologies.     

Synthesis of Sm-doped strontium barium niobate crystals in glass by samarium atom heat processing

New glasses giving the crystallization of Sm³⁺-doped Sr_xBa_1−xNb₂O₆ (SBN) ferroelectrics have been developed in the Sm₂O₃−SrO−BaO−Nb₂O₅−B₂O₃ system, and the formation of SBN crystal dots and lines by continuous wave Nd:YAG laser (wavelength:1064 nm, power: 1 W) irradiations, i.e., samarium atom heat processing, has been examined. The formation of Sm³⁺-doped SBN non-linear optical crystals is confirmed from X-ray diffraction analyses, micro-Raman scattering spectra, second harmonic generations, and photoluminescence spectra. Sm³⁺-doped SBN crystal dots with the diameters of 20-70 μm and lines with the widths of 20-40 μm are written at the surface of some glasses such as 10Sm₂O₃·10SrO·10BaO·20Nb₂O₅·50B₂O₃ (mol%) by Nd:YAG laser irradiations with the irradiation times of 20-70 s for the dots and with the scanning speeds of 1-5 μm/s for the lines. The present study suggests that the samarium atom heat processing has a potential for the patterning of optical waveguides consisting of ferroelectric SBN crystals in glass substrates.     

Spatially selected synthesis of LaF3 and Er-doped CaF2 crystals in oxyfluoride glasses by laser-induced crystallization

Oxyfluoride glasses with a small amount of NiO are prepared using a conventional melt quenching technique, and the spatially selected crystallization of LaF₃ and CaF₂ crystals is induced on the glass surface by irradiations of continuous wave lasers with a wavelength of λ=1064 or 1080 nm. Dots and lines including LaF₃ crystals are patterned by heat-assisted (300 °C) laser irradiations (λ=1064 nm) with a power of P=1 W and an irradiation time of 10 s for dots and a scanning speed of S=5 μm/s for lines. Lines consisting of CaF₂ crystals are also patterned in an ErF₃-doped oxyfluoride glass by laser irradiations (λ=1080 nm) with a power of P=1.7 W and a scanning speed of S=2 μm/s, and the incorporation of Er³⁺ ions into CaF₂ crystals is confirmed from micro-photoluminescence spectrum measurements. It is proposed that the lines patterned by laser irradiations in this study are consisted of the composite of LaF₃ or CaF₂ nanocrystals and SiO₂-based oxide glassy phase. It is demonstrated that a combination of Ni²⁺-dopings and laser irradiations is effective in spatially selected local crystallizations of fluorides in oxyfluoride glasses.     

Ion-beam irradiation of lanthanum compounds in the systems La2O3-Al2O3 and La2O3-TiO2

Thin crystals of La₂O₃, LaAlO₃, La_2/3TiO₃, La₂TiO₅, and La₂Ti₂O₇ have been irradiated in situ using 1 MeV Kr²⁺ ions at the Intermediate Voltage Electron Microscope-Tandem User Facility (IVEM-Tandem), Argonne National Laboratory (ANL). We observed that La₂O₃ remained crystalline to a fluence greater than 3.1×10¹⁶ ions cm⁻² at a temperature of 50 K. The four binary oxide compounds in the two systems were observed through the crystalline-amorphous transition as a function of ion fluence and temperature. Results from the ion irradiations give critical temperatures for amorphisation (T_c) of 647 K for LaAlO₃, 840 K for La₂Ti₂O₇, 865 K for La_2/3TiO₃, and 1027 K for La₂TiO₅. The T_c values observed in this study, together with previous data for Al₂O₃ and TiO₂, are discussed with reference to the melting points for the La₂O₃-Al₂O₃ and La₂O₃-TiO₂ systems and the different local environments within the four crystal structures. Results suggest that there is an observable inverse correlation between T_c and melting temperature (T_m) in the two systems. More complex relationships exist between T_c and crystal structure, with the stoichiometric perovskite LaAlO₃ being the most resistant to amorphisation.     

Effect of sintering on the ionic conductivity of garnet-related structure Li5La3Nb2O12 and In- and K-doped Li5La3Nb2O12

Garnet-structure related metal oxides with the nominal chemical composition of Li₅La₃Nb₂O₁₂, In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ and K-substituted Li_5.5La_2.75K_0.25Nb₂O₁₂ were prepared by solid-state reactions at 900, 950, and 1000 °C using appropriate amounts of corresponding metal oxides, nitrates and carbonates. The powder XRD data reveal that the In- and K-doped compounds are isostructural with the parent compound Li₅La₃Nb₂O₁₂. The variation in the cubic lattice parameter was found to change with the size of the dopant ions, for example, substitution of larger In³⁺(r_CN6: 0.79 Å) for smaller Nb⁵⁺ (r_CN6: 0.64 Å) shows an increase in the lattice parameter from 12.8005(9) to 12.826(1) Å at 1000 °C. Samples prepared at higher temperatures (950, 1000 °C) show mainly bulk lithium ion conductivity in contrast to those synthesized at lower temperatures (900 °C). The activation energies for the ionic conductivities are comparable for all samples. Partial substitution of K⁺ for La³⁺ and In³⁺ for Nb⁵⁺ in Li₅La₃Nb₂O₁₂ exhibits slightly higher ionic conductivity than that of the parent compound over the investigated temperature regime 25-300 °C. Among the compounds investigated, the In-substituted Li_5.5La₃Nb_1.75In_0.25O₁₂ exhibits the highest bulk lithium ion conductivity of 1.8×10⁻⁴ S/cm at 50 °C with an activation energy of 0.51 eV. The diffusivity (“component diffusion coefficient”) obtained from the AC conductivity and powder XRD data falls in the range 10⁻¹⁰-10⁻⁷ cm²/s over the temperature regime 50-200 °C, which is extraordinarily high and comparable with liquids. Substitution of Al, Co, and Ni for Nb in Li₅La₃Nb₂O₁₂ was found to be unsuccessful under the investigated conditions.     

Preparation and photoluminescence properties of RE:Na3La9O3(BO3)8 (RE=Er, Yb) crystals

Using Na₂CO₃-H₃BO₃-NaF as fluxes, transparent RE:Na₃La₉O₃(BO₃)₈ (abbr. RE:NLBO, RE=Er, Yb) crystals have been grown by the top seed solution growth (TSSG) method. The X-ray powder diffraction analysis shows that the RE:NLBO crystals have the same structure with NLBO. The element contents were determined by molar to be 0.64% Er³⁺ in Er:NLBO, 2.70% Yb³⁺ in Yb:NLBO, respectively. The polarized absorption spectra of RE:NLBO have been measured at room temperature and show that both Er:NLBO and Yb:NLBO have a strong absorption bands near 980 nm with wide FWHM (Full Wave at Half Maximum) (21 nm for Er:NLBO and 25 nm for Yb:NLBO). Fluorescence spectra have been recorded. Yb:NLBO has the emission peaks at 985 nm, 1028 nm and 1079 nm and the emission peak of Er:NLBO is at 1536 nm. Spectral parameters have been calculated by the Judd-Ofelt theory for Er:NLBO and the reciprocity method for Yb:NLBO, respectively. The calculated values show that Er:NLBO is a candidate of 1.55 μm laser crystals and Yb:NLBO is a candidate for self-frequency doubling crystal.     

Synthesis and magnetic properties of rare earth ruthenates, Ln5Ru2O12 (Ln=Pr, Nd, Sm-Tb)

Single crystals of Ln₅Ru₂O₁₂ (Ln=Pr, Nd, Sm-Tb) were grown out of either NaOH or KOH fluxes in sealed silver tubes. The crystals of all the phases were observed to be twinned as confirmed by TEM studies. The series crystallize in the C2/m monoclinic system with lattice parameters, a=12.4049(4)-12.7621(6) Å, b=5.8414(2)-5.9488(3) Å, c=7.3489(2)-7.6424(4) Å, β=107.425(3)-107.432(2)° and Z=2. The crystal structure is isotypic with the defect/disorder model of Ln₅Re₂O₁₂ (Ln = Y, Gd) and consists of one dimensional edge shared RuO₆ octahedral chains separated by a two dimensional LnO_x polyhedral framework. Magnetic measurements indicate paramagnetic and antiferromagnetic behavior for Ln=Nd, Sm-Gd and Ln=Tb, respectively.     

Growth of La2CuO4 nanofibers under a mild condition by using single walled carbon nanotubes as templates

La₂CuO₄ nanofibers (ca. 30 nm in diameter and 3 μm in length) have been grown in situ by using single walled carbon nanotubes (SWNTs; ca. 2 nm in inner diameter; made via cracking CH₄ over the catalyst of Mg_0.8Mo_0.05Ni_0.10Co_0.05O_x at 800 °C) as templates under mild hydrothermal conditions and a temperature around 60 °C. During synthesis, the surfactant poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) and H₂O₂ were added to disperse SWNTs and oxidize the reactants, respectively. The structure of La₂CuO₄ nanofibers was confirmed by powder X-ray diffraction (XRD) and their morphologies were observed with field emission scanning electron microscope (FESEM) at the hydrothermal synthesis lasting for 5, 20 and 40 h, respectively. The La₂CuO₄ crystals grew from needle-like (5 h) through stick-like (20 h) and finally to plate-like (40 h) fibers. Twenty hours is an optimum reaction time to obtain regular crystal fibers. The La₂CuO₄ nanofibers are probably cubic rather than round and may capsulate SWNTs.     

Origin of periodic domain structure in Er-doped β′-(Sm,Gd)2(MoO4)3 crystal lines patterned by laser irradiations in glasses

Er³⁺-doped β′-(Sm,Gd)₂(MoO₄)₃ crystal lines are patterned on the surface of Er₂O₃-Gd₂O₃-Sm₂O₃-MoO₃-B₂O₃ glasses by continuous-wave Yb:YVO₄ laser irradiations (wavelength: 1080 nm, power: 1.3 W, scanning speeds: 5 μm/s), and the origin of the periodicity of self-organized domain structures with high and low refractive index regions in crystal lines is examined from polarized optical microscope (POM) observations, micro-Raman scattering spectrum, and photoluminescence spectrum measurements. It is found that the periodicity of domain structures changes largely depending on Er₂O₃ content, i.e., the length of high (bright color in POM observations) and low (dark color) refractive index regions increases with increasing Er₂O₃ content and homogeneous crystal lines with no periodic domain structures are patterned in Er₂O₃-Sm₂O₃-MoO₃-B₂O₃ glass with no Gd₂O₃. Considering that the degree of ferroelasticities in β′-(Sm,Gd)₂(MoO₄)₃ crystals decreases due to the incorporation of Er³⁺ ions, it is demonstrated that the origin of periodic domain structures in laser-patterned lines is due to spontaneous strains in ferroelastic β′-(Sm,Gd)₂(MoO₄)₃ crystals.     

Synthesis, structure and electrical properties of Cu3.21Ti1.16Nb2.63O12 and the CuOx-TiO2-Nb2O5 pseudoternary phase diagram

Subsolidus phase relations in the CuO_x-TiO₂-Nb₂O₅ system were determined at 935 °C. The phase diagram contains one new phase, Cu_3.21Ti_1.16Nb_2.63O₁₂ (CTNO) and one rutile-structured solid solution series, Ti_1−3xCu_xNb_2xO₂: 0<x<0.2335 (35). The crystal structure of CTNO is similar to that of CaCu₃Ti₄O₁₂ (CCTO) with square planar Cu²⁺ but with A site vacancies and a disordered mixture of Cu⁺, Ti⁴⁺ and Nb⁵⁺ on the octahedral sites. It is a modest semiconductor with relative permittivity ∼63 and displays non-Arrhenius conductivity behavior that is essentially temperature-independent at the lowest temperatures.     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.     

Phase relations, crystal chemistry, and dielectric properties in sections of the La2O3-CaO-MgO-TiO2 system

Subsolidus phase equilibria and crystal chemistry were studied for the La₂O₃-MgO-TiO₂ system and for the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃ in the quaternary La₂O₃-CaO-MgO-TiO₂ system. Dielectric properties (relative permittivity and temperature coefficient of resonant frequency, τ_f) were measured at 5-10 GHz and mapped onto the phase equilibria relations to reveal the compositions of temperature-stable (τ_f=0) compounds and mixtures. Phase equilibria relations were obtained by X-ray powder diffraction analysis of approximately 80 specimens prepared by solid-state reactions in air at ∼1450°C. Six ternary phases were found to form in the La₂O₃-MgO-TiO₂ system, including the three previously reported compounds LaMg_1/2Ti_1/2O₃, La₅Mg_0.5Ti_3.5O₁₅, and “La₆MgTi₄O₁₈”; and the new phases La₁₀MgTi₉O₃₄, La₉Mg_0.5Ti_8.5O₃₁, and a perovskite-type solid solution (1−x)LaMg_1/2Ti_1/2O₃-xLa_2/3TiO₃ (0?x?0.5). The phase previously reported as “La₆MgTi₄O₁₈” was found to form off-composition, apparently as a point compound, at La₆Mg_0.913Ti_4.04O₁₈. Indexed experimental X-ray powder diffraction patterns are given for LaMg_1/2Ti_1/2O₃, La₅Mg_0.5Ti_3.5O₁₅, La₆Mg_0.913Ti_4.04O₁₈, La₁₀MgTi₉O₃₄, and La₉Mg_0.5Ti_8.5O₃₁. LaMg_1/2Ti_1/2O₃ exhibits a slightly distorted perovskite structure with ordered B-cations (P2₁/n; a=5.5608(2) Å, b=5.5749(3) Å, c=7.8610(5) Å, β=90.034(4)°). La₅Mg_0.5Ti_3.5O₁₅ (Pm1; a=5.5639(1), c=10.9928(5) Å) and La₆Mg_0.913Ti_4.04O₁₈ (R3m; a=5.5665(1), c=39.7354(9) Å) are n=5 and n=6 members, respectively, of the (111) perovskite-slab series A_nB_n−1O_3n. The new phases La₁₀MgTi₉O₃₄ (a=5.5411(2), b=31.3039(9), c=3.9167(1) Å) and La₉Mg_0.5Ti_8.5O₃₁ (a=5.5431(2), b=57.055(1), c=3.9123(1) Å) are n=5 and n=4.5 members, respectively, of the (110) perovskite-slab series A_nB_nO_3n+2, which exhibit orthorhombic subcells; electron diffraction revealed monoclinic superlattices with doubled c-parameters for both compounds. Extensive perovskite-type solid solutions form in the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃. The La₂O₃-MgO-TiO₂ system contains two regions of temperature-stable (τ_f=0) compositions. The quaternary La₂O₃-CaO-MgO-TiO₂ system contains an extensive single-phase perovskite-type volume through which passes a surface of temperature-stable compositions with permittivities projected to be in the 40-50 range. Traces of this surface occur as lines of τ_f=0 perovskite-type phases in the ternary sections LaMg_1/2Ti_1/2O₃-CaTiO₃-La₂O₃ and LaMg_1/2Ti_1/2O₃-CaTiO₃-La_0.833Mg_0.25Ti_0.75O₃.     

Synthesis, structures and photocatalytic activities of microcrystalline ABi2Nb2O9 (A=Sr, Ba) powders

Microcrystalline ABi₂Nb₂O₉ (A=Sr, Ba) photocatalysts were successfully synthesized by a citrate complex method. The as-prepared samples were characterized by the X-ray diffraction technique, BET surface area analysis, UV-vis diffuse reflectance spectrum, transmission electron microscopy, X-ray photoelectron spectroscopy and inductively coupled plasma-atomic emission spectrometry. The results indicated that single-phase orthorhombic SrBi₂Nb₂O₉ could be obtained after being calcined above 650 °C, while BaBi₂Nb₂O₉ was tetragonal. Based on the diffuse reflectance spectra, the band gaps of the obtained samples were calculated to be around 3.34-3.54 eV. For the photocatalytic redox reaction of methyl orange under UV-light irradiation, SrBi₂Nb₂O₉ exhibited higher photocatalytic activity than that of BaBi₂Nb₂O₉. The effects of the crystallinities, BET surface areas and crystal structures of the samples on the photocatalytic activities were discussed in detail.     

Contrasting oxide crystal chemistry of Nb and Ta:: The structures of the hexagonal bronzes BaTa2O6 and Ba0.93Nb2.03O6

The high-temperature hexagonal forms of BaTa₂O₆ and Ba_0.93Nb_2.03O₆ have P6/mmm symmetry with unit-cell parameters a=21.116(1) Å, c=3.9157(2) Å and a=21.0174(3) Å, c=3.9732(1) Å, respectively. Single crystal X-ray structure refinements for both phases are generally consistent with a previously proposed model, except for displacements of some Ba atoms from high-symmetry positions. The structures are based on a framework of corner- and edge-connected Nb/Ta-centred octahedra, with barium atoms occupying sites in four different types of [0 0 1] channels with hexagonal, triangular, rectangular and pentagonal cross-sections. The refinements showed that the non-stoichiometry in the niobate phase is due to barium atom vacancies in the pentagonal channels and to extra niobium atoms occupying interstitial sites with tri-capped trigonal prismatic coordination. The origin of the non-stoichiometry is attributed to minimisation of non-bonded Ba-Ba repulsions. The hexagonal structure is related to the structures of the low-temperature forms of BaNb₂O₆ and BaTa₂O₆, through a 30° rotation of the hexagonal rings of octahedra centred at the origin.     

Crystal structure, stoichiometry, and dielectric relaxation in Bi3.32Nb7.09O22.7 and structurally related ternary phases

The crystal structure of the phase previously reported to occur at 4:9 Bi₂O₃:Nb₂O₅ has been determined using single-crystal X-ray and powder neutron diffraction (P6₃/mmc; a=7.4363(1) Å, c=19.7587(5) Å; Z=2). The structural study combined with phase equilibrium analyses indicate that the actual composition is Bi_3.32Nb_7.09O_22.7. This binary compound is the end-member of a family of four phases which form along a line between it and the pyrochlore phase field in the Bi₂O₃:Fe₂O₃:Nb₂O₅ system. The structures are derived from the parent pyrochlore end-member by chemical twinning, and can also be described as unit-cell intergrowths of the pyrochlore and hexagonal tungsten bronze (HTB) structures. The dielectric properties of the three chemically twinned pyrochlore phases, Bi_3.32Nb_7.09O_22.7, Bi_9.3Fe_1.1Nb_16.9O_57.8 and Bi_5.67FeNb₁₀O₃₅, were characterized. All exhibit low-temperature, broad dielectric relaxation similar to that of the Bi-Fe-Nb-O pyrochlore. At 1 MHz and ≈175 K the observed relative permittivites were 345, 240, and 205, respectively, compared to 125 for the Bi-Fe-Nb-O pyrochlore. The higher relative permittivities observed for the chemically twinned pyrochlore derivatives are ascribed to the presence of HTB blocks in their structures: The Bi atoms located in the HTB blocks feature highly asymmetric coordination environments compared to pyrochlore, and the magnitude of the relative permittivity increases with the proportion of Bi located within the HTB portions of the structures.     

La3Ru8B6 and Y3Os8B6, new members of a homologous series R(A)nM3n−1B2n

Two new compounds, La₃Ru₈B₆ and Y₃Os₈B₆, were synthesized by arc melting the elements. Their structural characterization was carried out at room temperature on as-cast samples by using X-ray diffractometry. According to X-ray single-crystal diffraction results these borides crystallize in Fmmm space group (no. 69), Z=4, a=5.5607(1) Å, b=9.8035(3) Å, c=17.5524(4) Å, ρ=8.956 Mg/m³, μ=25.23 mm⁻¹ for La₃Ru₈B₆ and a=5.4792(2) Å, b=9.5139(4) Å, c=17.6972(8) Å, ρ=13.343 Mg/m³, μ=128.23 mm⁻¹ for Y₃Os₈B₆. The crystal structure of La₃Ru₈B₆ was confirmed from Rietveld refinement of X-ray powder diffraction data. Both La₃Ru₈B₆ and Y₃Os₈B₆ compounds are isotypic with the Ca₃Rh₈B₆ compound and their structures are built up from CeCo₃B₂-type and CeAl₂Ga₂-type structural fragments taken in ratio 2:1. They are the members of structural series R(A)_nM_3n−1B_2n with n=3 (R is the rare earth metal, A the alkaline earth metal, and M the transition metal). Structural and atomic parameters were also obtained for La_0.94Ru₃B₂ compound from Rietveld refinement (CeCo₃B₂-type structure, P6/mmm space group (no. 191), a=5.5835(9) Å, c=3.0278(6) Å).     

Crystal growth, structural characterization and magnetic properties of Ca3CuRhO6, Ca3Co1.34Rh0.66O6 and Ca3FeRhO6

Single crystals of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ were synthesized by high temperature flux growth in molten K₂CO₃ and structurally characterized by single crystal X-ray diffraction. While Ca₃Co_1.34Rh_0.66O₆ and Ca₃FeRhO₆ crystallize with trigonal (rhombohedral) symmetry in the space group , Z=6: Ca₃Co_1.34Rh_0.66O₆a=9.161(1) Å, c=10.601(2) Å; Ca₃FeRhO₆a=9.1884(3) Å, c=10.7750(4) Å; Ca₃CuRhO₆ adopts a monoclinic distortion of the K₄CdCl₆ structure in the space group C2/c, Z=4: a=9.004(2) Å, b=9.218(2) Å, c=6.453(1) Å, β=91.672(5). All crystals of Ca₃CuRhO₆ examined were twinned by pseudo-merohedry. Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are structurally related and contain infinite one-dimensional chains of alternating face-sharing RhO₆ octahedra and MO₆ trigonal prisms. In the monoclinic modification, the copper atoms are displaced from the center of the trigonal prism toward one of the rectangular faces adopting a pseudo-square planar configuration. The magnetic properties of Ca₃CuRhO₆, Ca₃Co_1.34Rh_0.66O₆, and Ca₃FeRhO₆ are discussed.     

Direct syntheses of Lan+1NinO3n+1 phases (n=1, 2, 3 and ∞) from nanosized co-crystallites

A new direct route for the “bottom up” syntheses of phases in the La_n+1Ni_nO_3n+1 series (n=1, 2, 3 and ∞) has been achieved via single-step heat treatments of nanosized co-crystallized precursors. The co-crystallized precursors were prepared using a continuous hydrothermal flow synthesis system that uses a superheated water flow at ca. 400 °C and 24.1 MPa to produce nanoparticulate slurries. Overall, a significant reduction in time and number of steps for the syntheses of La₃Ni₂O₇ and La₄Ni₃O₁₀ was achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.     

Structural and magnetic properties of the quaternary oxides Ba6Ln2Fe4O15 (Ln=Pr and Nd)

The crystal structures and magnetic properties of the quaternary lanthanide oxides Ba₆Ln₂Fe₄O₁₅ (Ln=Pr and Nd) are reported. They crystallize in a hexagonal structure with space group P6₃mc and have the “Fe₄O₁₅ cluster” consisting of one FeO₆ octahedron and three FeO₄ tetrahedra. Measurements of the magnetic susceptibility, specific heat, and powder neutron diffraction reveal that this cluster behaves as a spin tetramer with a ferrimagnetic ground state of S_T=5 even at room temperature. The cluster moments show a long-range antiferromagnetic ordering at 23.2 K (Ln=Pr) and 17.8 K (Nd), and the magnetic moments of the Ln³⁺ ions also order cooperatively. By applying the magnetic field (∼2 T), this antiferromagnetic ordering of the clusters changes to a ferromagnetic one. This result indicates that there exists a competition in the magnetic interaction between the clusters.