Flux growth of crystals of some transition metal fluorides

The flux growth of crystals of the following complex fluorides is reported: KAlF₄, KMnF₃, RbFeF₄, Rb₂FeF₅, Rb₃FeF₆, Rb _x FeF₃ (0.18<x<0.29), CsFeF₄, CsFe₂F₇, Cs₃Fe₂F₉, Cs _x FeF₃ (0.18<x<0.29), Na₂CoFeF₇, Na₂NiFeF₇, Na₂NiAlF₇, Na₂ZnCrF₇, NaCrF₄ and Rb₂Cr₅F₁₇. Flux impurity levels, determined by electron probe microanalysis (EPMA), were low. However, attempts to produce BaNiF₄, BaCoF₄, CsCrF₄ and Cs₂Cr₅F₁₇ resulted in crystals with higher levels of substitutional impurities. X-ray powder patterns and EPMA were used to characterize the crystals.     

Flux growth of crystals of some transition metal fluorides

The flux growth of crystals of the following complex fluorides is reported: KFeF₄, K₂FeF₅, K₂Fe₅F₁₇, RbFeF₄, FeF₃, K_0.25FeF₃, K₂CrF₅, KCrF₄, K₂Cr₅F₁₇, K₂NiF₄, KNiF₃ and LiRF₅ (R=Er to Gd). Triangular composition diagrams for the metal fluoride, KF, and KCl or PbCl₂ are given.     

Flux growth of crystals of some transition metal fluorides

The flux growth of the following complex fluorides is reported: KNiCrF₆; RbCoCrF₆, RbMnCrF₆; CsCoAIF₆, CsCoCrF₆, CsCoFeF₆; CsCrAIF₆; CsMgAIF₆, CsMgCrF₆, CsMgFeF₆; CsMnAIF₆, CsMnCrF₆, CsMnFeF₆; CsNiAIF₆, CsNiCrF₆, CsNiFeF₆; CsZnFeF₆. Octahedral crystals of some of these materials with edges up to 1 cm have been grown. Most of them are cubic, but several are twinned, indicating a structural phase transition below the growth temperature. The growth of KCr₂ F_6.5 and BaNiF_3.6Cl_0.4 crystals is also described. Larger faceted crystals of K₂FeF₅ are reported. The growth of crystals of KFe₂F₆, previously only prepared under HF and N₂, has been achieved in air.     

The flux growth of some rare-earth and iron group complex oxides

The flux growth of crystals of the following rare-earth complex oxides is reported here for the first time: (Nd, Pb)MnO₃, (Eu, Pb)MnO₃. Tm₂Ge₂O₇ and Pr₂MoO₆. Starting compositions for the flux growth of RBO₃ (R=Nd, Pr, La), (La, Pb)MnO₃, Pb₃Mn₇O₁₅, R₂Ti₂O₇ (R=Tm to Pr), R₂SiO₅ (R=Er, Ho, Dy) and LiCoPO₄ are also given; these compositions have yielded larger crystals than previously reported. In many cases, only a small number of crystals was obtained by spontaneous nucleation.     

Flux growth of large YAG crystals

Large yttrium and rare earth aluminum garnet crystals that are essentially free of flux pockets, veils or discoloration due to dispersed Pb can be grown from a PbO·PbF₂·B₂O₃ flux as a cluster alone or surrounded by plates of sapphire or ruby in a rosette fashion. Quality is improved by growth in the presence of massive Al₂O₃ at a high temperature.     

Microstructure and growth mechanism of stressed complex oxide thin films in strain-modulation

A series of experiments of strain modulations in heterostructures of SrTiO₃/LaAlO₃ and LaAlO₃/SrTiO₃ perovskite thin films fabricated by laser molecular beam epitaxy (L-MBE) were performed to study the effect of the compressive stress and tensile stress on the growth and microstructure of the films. The growth process of the films was in-situ monitored by reflective high-energy electron diffraction (RHEED). The morphology of the films was studied by ex-situ atomic force microscopy (AFM). We demonstrated that the compressive stress-induced self-organized SrTiO₃ films deposited on LaAlO₃ (100) single crystal substrates exhibited a periodic well-ordered ripple-shaped structure, forming a unique nanopatterning tool to fabricate 1D/2D arrays of confined nanostructures (i.e., islands and wires). Small angle X-ray scattering technique was employed to investigate the superstructure. Symmetric satellite peaks were observed, which also revealed the well-aligned self-organized structures. In contrast, the similar superstructure was not observed during the growth of the tensile stress-induced LaAlO₃ films on SrTiO₃ substrates. Based on the experimental data, the compressive stress was estimated as the main reason of the self-organized growth. A growth model about the formation mechanisms of compressive stress-induced nanostructure was put forward and systematical kinetics elucidations about the growth processes were also discussed to illustrate the effects of different stresses on the growth and microstructures of the films.     

Flux growth of the rare earth germanates

The growth of the compounds R₂Ge₂O₇ from lead fluoride flux, and of R₂Ge₂O₇ and R₂GeO₅ from lead germanate fluxes, is described (R=Tb to Lu). The magnetic transition temperatures are given.     

Flux growth and characterization of TiC crystals

Single crystals of TiC were grown using nickel and cobalt metal as a flux at soaking temperatures of 1500 to 1800° C and at compositions of 12.5 to 30 mol% TiC. The use of cobalt flux produced crystal sizes less than 0.5 mm under all conditions. With a nickel flux, a maximum crystal size of 1.5 mm was obtained at 1700 and 1800°C and at 20 and 25 mol% TiC composition, using a cooling rate of 3° C min^–1. A slower cooling rate of 0.2° C min^–1 also gave crystals of 1.5 mm at 1600° C. The crystals were cubic and metallic-lustre silver grey in colour. The lattice parameter of the crystal was measured to bea ₀ = 0.432 75 ± 0.000 05 nm, with nearly stoichiometric composition. The grown faces were of the {1 0 0} family with a dislocation density around 10⁷ cm^-2. The Vickers' microhardness on these faces was in the range 2600 to 2800 kg mm^–2. The nickel impurity and free carbon contents in the crystals were 700 to 1000 p.p.m. and 0.8 to 4 wt%, respectively.     

Crystal growth of oxide and fluoride materials for optical, piezoelectric and other applications

High quality oxide and fluoride single crystals for optical, piezoelectric and other applications have been grown by advanced crystal growth techniques. La₃Nb_0.5Ga_5.5O₁₄ and La₃Ta_0.5Ga_5.5O₁₄ piezoelectric single crystals of size and quality comparable to La₃Ga₅SiO₁₄ (langasite), have been produced. The piezoelectric and device properties of the crystals were investigated. A search for new langasite-type materials was also performed. Growth conditions of (La,Sr)(Al,Ta)O₃ and Ca₈La₂(PO₄)₆O₂ single crystals are discussed. These crystals have excellent lattice matching with GaN, a promising material for optoelectronic devices. Promising optical micro-crystals—K₃Li₂Nb₅O₁₅, KNbO₃ and Y₃Al₅O₁₂—and new structural materials, Al₂O₃Y₃Al₅O₁₂ eutectic fibers, have been grown by the micro-pulling-down (-PD) technique. The advantages of the -PD technique have been shown. Ce-doped fluoride single crystals—LiCaAlF₆, LiYF₄ and BaLiF₃—have been grown for solid state UV laser applications. Growth results and optical characterizations are discussed.     

The flux growth of some new rare earth and iron group complex oxides

The flux growth of crystals of a number of new rare-earth and transition metal compounds is reported. The following empirical formulae were in good agreement with electron probe microanalysis (EPMA): (Ba, Gd)TiO₃, R₄Ba₆(BO₃)₉(R = Ho to La), Ni₃Nb₂O₈, Ni₈NbB₃O₁₅, Ni₂V₂PbO₈, Ta₂Co₄O₉ and PbCr_2.3Ti_2.3O₉. X-ray powder pattern data are given. The growth of crystals of GdVO₃, Pb₂CrO₅ and Ni₃V₂O₈, which have previously been prepared only as powders, is also reported.     

氧化物热电材料的研究进展

介绍了氧化物热电材料的研究现状及发展趋势,以及氧化物热电材料的特殊优点;同时对氧化物热电材料做了大致分类.深入介绍了关于错配层氧化物高热电势起因的最新研究成果;广泛介绍了perovskite结构氧化物的置换对热电性能的影响,探讨了其导电机理及热电势的可能起因.最后介绍了透明导电氧化物热电材料.