Synthesis and nonlinear optical properties of BaTi(BO3)2 and Ba3Ti3O6(BO3)2 crystals in glasses with high TiO2 contents

The ternary BaO-TiO₂-B₂O₃ glasses containing a large amount of TiO₂ (20-40 mol%) are prepared, and their optical basicities (Λ), the formation, structural features and second-order optical nonlinearities of BaTi(BO₃)₂ and Ba₃Ti₃O₆(BO₃)₂ crystals are examined to develop new nonlinear optical materials. It is found that the glasses with high TiO₂ contents of 30-40 mol% show large optical basicities of Λ=0.81-0.87, suggesting the high polarizabity of TiO_n polyhedra (n=4-6) in the glasses. BaTi(BO₃)₂ and Ba₃Ti₃O₆(BO₃)₂ crystals are found to be formed as main crystalline phases in the glasses. It is found that BaTi(BO₃)₂ crystals tend to orient at the surface of crystallized glasses. The new XRD pattern for the Ba₃Ti₃O₆(BO₃)₂ phase is proposed through Rietvelt analysis. The second harmonic intensities of crystallized glasses were found to be 0.8 times as large as α-quartz powders, i.e., I^2ω(sample)/I^2ω(α-quartz)=0.8, for the sample with BaTi(BO₃)₂ crystals and to be I^2ω(sample)/I^2ω(α-quartz)=68 for the sample with Ba₃Ti₃O₆(BO₃)₂ crystals. The Raman scattering spectra for these two crystalline phases are measured for the first time and their structural features are discussed.     

MAS-NMR investigations of the crystallization behaviour of lithium aluminum silicate (LAS) glasses containing P2O5 and TiO2 nucleants

Lithium aluminum silicate (LAS) glass of composition (mol%) 20.4Li₂O-4.0Al₂O₃-68.6SiO₂-3.0K₂O-2.6B₂O₃-0.5P₂O₅-0.9TiO₂ was prepared by melt quenching. The glass was then nucleated and crystallized based on differential thermal analysis (DTA) data and was characterized by ²⁹Si, ³¹P, ¹¹B and ²⁷Al MAS-NMR. XRD and ²⁹Si NMR showed that lithium metasilicate (Li₂SiO₃) is the first phase to c form followed by cristobalite (SiO₂) and lithium disilicate (Li₂Si₂O₅). ²⁹Si MAS-NMR revealed a change in the network structure already for the glasses nucleated at 550 °C. Since crystalline Li₃PO₄, as observed by ³¹P MAS-NMR, forms concurrently with the silicate phases, we conclude that crystalline Li₃PO₄ does not act as a nucleating agent for lithium silicate phases. Moreover, ³¹P NMR indicates the formation of M-PO₄ (M=B, Al or Ti) complexes. The presence of BO₃ and BO₄ structural units in all the glass/glass-ceramic samples is revealed through ¹¹B MAS-NMR. B remains in the residual glass and the crystallization of silicate phases causes a reduction in the number of alkali ions available for charge compensation. As a result, the number of trigonally coordinated B (BO₃) increases at the expense of tetrahedrally coordinated B (BO₄). The ²⁷Al MAS-NMR spectra indicate the presence of tetrahedrally coordinated Al species, which are only slightly perturbed by the crystallization.     

The effect of TiO2 on the structure and devitrification behavior of potassium titanium germanate glass

The effect of replacing 20 mol% of GeO₂ by TiO₂ on the properties of potassium germanate glass was investigated. The structure and devitrification behaviour of glasses were studied by Fourier transform infrared spectroscopy (FTIR), differential thermal analysis (DTA) and X-ray diffraction (XRD). It was observed that potassium titanium germanate has a higher glass transition temperature and a higher thermal stability vs. crystallization. The presence of two exothermic peaks on the DTA curve of potassium germanate glass indicates the complex crystallization process. The XRD pattern of this glass heated at the temperature of the first crystallization peak indicated that the GeO₂ and K₂Ge₇O₁₅ were formed. Only the K₂TiGe₃O₉ phase was identified, in a case when potassium titanium germanate glass was heated at the temperature of the crystallization peak.     

Synthesis of nanocrystals in KNb(Ge,Si)O5 glasses and chemical etching of nanocrystallized glass fibers

The nanocrystallization behavior of 25K₂O−25Nb₂O₅-(50−x)GeO₂-xSiO₂ glasses with x=0,25,and50 (i.e., KNb(Ge,Si)O₅ glasses) and the chemical etching behavior of transparent nanocrystallized glass fibers have been examined. All glasses show nanocrystallization, and the degree of transparency of the glasses studied depends on the heat treatment temperature. Transparent nanocrystallized glasses can be obtained if the glasses are heat treated at the first crystallization peak temperature. Transparent nanocrystallized glass fibers with a diameter of about 100 μm in 25K₂O-25Nb₂O₅-50GeO₂ are fabricated, and fibers with sharpened tips (e.g., the taper length is about 450 μm and the tip angle is about 12°) are obtained using a meniscus chemical etching method, in which etching solutions of 10 wt%-HF/hexane and 10 M-NaOH/hexane are used. Although the tip (aperture size) has not a nanoscaled size, the present study suggests that KNb(Ge,Si)O₅ nanocrystallized glass fibers have a potential for new near-field optical fiber probes with high refractive indices of around n=1.8 and high dielectric constants of around ε=58 (1 kHz, room temperature).     

A Structural Investigation of La2(GeO4)O and Alkaline-Earth-Doped La9.33(GeO4)6O2

The structures of the oxyorthogermanate La₂(GeO₄)O and the apatite-structured La_9.33(GeO₄)₆O₂ have been refined from powder neutron diffraction data. La₂(GeO₄)O crystallizes in a monoclinic unit cell (P2₁/c) and is cation stoichiometric in contrast to previous reports. La_9.33(GeO₄)₆O₂ crystallizes in a hexagonal unit cell (P6₃/m) and the powder diffraction data show anisotropic peak broadening that is observed in electron diffraction patterns as incommensurate diffuse spots at hkq reciprocal planes (with q=1.6-1.7) and can be attributed to a correlated disorder in the “apatite channels”. This compound was doped up to a nominal composition close to M₂La₈(GeO₄)₆O₂ with M=Ca, Sr, Ba. The dopant ions preferentially occupy the 4f sites as the number of La vacancies decreases. The measured ionic conductivity of La_9.33(GeO₄)₆O₂ is about 3 orders of magnitude larger than for La₂(GeO₄)O at high temperatures and decreases with increasing dopant content from the highest value of about 0.16 S cm⁻¹ at 1160 K.     

Structural studies in the BaO-B2O3-TiO2 system by XAS and B-NMR

The structure of barium-titanium-metaborate xBaO-xB₂O₃-yTiO₂ (y=0%, 4%, 8%, 16% and x=50-y/2) amorphous and crystallized powders, obtained using a polymeric precursor method, was investigated by Ti and B K-edge X-ray absorption spectroscopy (XAS) and ¹¹B-NMR high-resolution techniques. XANES study of amorphous samples shows that Ti⁴⁺ ions exist as ^[4]Ti species associated to ^[6]Ti and ^[5]Ti species in a practically equivalent amount. After crystallization, titanium environment is predominately composed by ^[6]Ti species. According to XANES results obtained at the B K-edge, the fraction of boron in tetrahedral sites (^[4]B) reduces as the amount of TiO₂ is increased from x=0% to 4%, with a consequent increase of boron in trigonal sites (^[3]B). By a combination of ¹¹B-NMR spin-echo and triple quantum magic angle spinning (3Q-MAS) techniques, the detailed borate speciation was determined as consisting in ^[4]B and two kind of trigonal sites, ^[3]B_A and ^[3]B_B, corresponding, respectively, to borates sharing three and two O atoms with other boron units. NMR results reveal not only the reduction in boron coordination also seen by XANES but also the simultaneous reduction in the condensation degree of trigonal units, when the Ti content is increased in the glass. In crystallized samples, β-BaB₂O₄ and BaTi(BO₃)₂ phases were identified and quantified by ¹¹B-NMR.     

Line patterning of (Sr,Ba)Nb2O6 crystals in borate glasses by transition metal atom heat processing

Some NiO-doped Bi₂O₃,La₂O₃-SrO-BaO-Nb₂O₅-B₂O₃ glasses giving the formation of strontium barium niobate Sr_0.5Ba_0.5Nb₂O₆ (SBN) crystals with a tetragonal tungsten-bronze structure through conventional crystallization in an electric furnace have been developed, and SBN crystal lines have been patterned on the glass surface by heat-assisted (250-300 °C) laser irradiation and scanning of continuous-wave Nd:YAG laser (wavelength: 1064 nm). The surface morphology and the quality of SBN crystal lines are examined from measurements of confocal scanning laser micrographs and polarized micro-Raman scattering spectra. The surface morphology of SBN crystal lines changes from periodic bump structures to homogeneous structures, depending on laser scanning conditions. It is suggested that the line patterned at the laser irradiation condition of laser power P=1 W and of laser scanning speed S=1 μm/s in 2NiO-4La₂O₃-16SrO-16BaO-32Nb₂O₅-30B₂O₃ glass has a possibility of the orientation of SBN crystals along the laser scanning direction. The present study demonstrates that the transition metal atom heat processing (i.e., a combination of cw Nd:YAG laser and Ni²⁺ ions) is a novel technique for spatially selected crystallization of SBN crystals in glass.     

Sol-gel synthesis of K3InF6 and structural characterization of K2InC10O10H6F9, K3InC12O14H4F18 and K3InC12O12F18

K₃InF₆ is synthesized by a sol-gel route starting from indium and potassium acetates dissolved in isopropanol in the stoichiometry 1:3, with trifluoroacetic acid as fluorinating agent. The crystal structures of the organic precursors were solved by X-ray diffraction methods on single crystals. Three organic compounds were isolated and identified: K₂InC₁₀O₁₀H₆F₉, K₃InC₁₂O₁₄H₄F₁₈ and K₃InC₁₂O₁₂F₁₈. The first one, deficient in potassium in comparison with the initial stoichiometry, is unstable. In its crystal structure, acetate as well as trifluoroacetate anions are coordinated to the indium atom. The two other precursors are obtained, respectively, by quick and slow evaporation of the solution. They correspond to the final organic compounds, which give K₃InF₆ by decomposition at high temperature. The crystal structure of K₃InC₁₂O₁₄H₄F₁₈ is characterized by complex anions [In(CF₃COO)₄(OH_x)₂]^(5−2x)− and isolated [CF₃COOH_2−x]^(x−1)− molecules with x=2 or 1, surrounded by K⁺ cations. The crystal structure of K₃InC₁₂O₁₂F₁₈ is only constituted by complex anions [In(CF₃COO)₆]³⁻ and K⁺ cations. For all these compounds, potassium cations ensure only the electroneutrality of the structure. IR spectra of K₂InC₁₀O₁₀H₆F₉ and K₃InC₁₂O₁₂F₁₈ were also performed at room temperature on pulverized crystals.     

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.     

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.     

The effect of B2O3 addition on the crystallization of amorphous TiO2-ZrO2 mixed oxide

The effect of B₂O₃ addition on the crystallization of amorphous TiO₂-ZrO₂ mixed oxide was investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA). TiO₂-ZrO₂ mixed oxide was prepared by co-precipitation method with aqueous ammonia as the precipitation reagent. Boric acid was used as a source of boria, and boria contents varied from 2 to 20 wt%. The results indicate that the addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO₂-ZrO₂ into a crystalline ZrTiO₄ compound, while a larger amount of boria (?8 wt%) promotes the crystallization process. FT-IR spectroscopy and ¹¹B MAS NMR results show that tetrahedral borate species predominate at low boria loading, and trigonal borate species increase with increasing boria loading. Thus it is concluded that highly dispersed tetrahedral BO₄ units delay, while a build-up of trigonal BO₃ promote, the crystallization of amorphous TiO₂-ZrO₂ to form ZrTiO₄ crystals.     

Pressure-induced structural transformations in lanthanide titanates: La2TiO5 and Nd2TiO5

The structure of orthorhombic rare earth titanates of La₂TiO₅ and Nd₂TiO₅, where Ti cations are in five-fold coordination with oxygen, has been studied at high pressures by X-ray diffraction (XRD), Raman scattering measurements, and quantum mechanical calculations. Both XRD and Raman results indicated two pressure-induced phase transitions during the process. An orthorhombic super cell (a×b×2c) formed at a pressure between 6 and 10 GPa, and then transformed to a hexagonal high-pressure phase accompanied by partial decomposition. The hexagonal high-pressure phase is quenchable. Detailed structural analysis indicated that the five-coordinated TiO₅ polyhedra remain during the formation of super cell, but the orthorhombic-to-hexagonal phase transition at high pressures is a reconstructive process, and the five-fold Ti-O coordination increased to more than 6. This phase transition sequence was verified by quantum mechanical calculations.     

Non-centrosymmetric Ba3Ti3O6(BO3)2

The compound previously reported as Ba₂Ti₂B₂O₉ has been reformulated as Ba₃Ti₃B₂O₁₂, or Ba₃Ti₃O₆(BO₃)₂, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO₃:BaTiB₂O₆ (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F²)=0.039 for 504 unique reflections. Ba₃Ti₃O₆(BO₃)₂ is isostructural with K₃Ta₃O₆(BO₃)₂. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba₃Ti₃O₆(BO₃)₂ is equal to 95% of that of LiNbO₃.     

三维有序大孔复合材料Bi2O3/TiO2制备与多模式下光催化降解结晶紫

以TiO2为基体,在聚苯乙烯(PS)胶球和EO20PO70EO20(P123)两种模板剂作用下通过溶胶-凝胶及煅烧后处理方法制备了三维有序大孔纳米复合材料Bi2O3/TiO2.经傅里叶变换红外(FT-IR)光谱、X-射线衍射(XRD)、等离子体原子发射光谱(ICP-AES)、紫外-可见漫反射吸收光谱(UV-Vis DRS)、X-射线光电子能谱(XPS)、扫描电子显微镜(SEM)和N2吸附-脱附等物理测试手段对其组成、结构、形貌及表面物理化学性能进行了表征.结果表明,该复合材料晶型结构良好,孔结构排列整齐有序,孔壁呈介孔结构,属于三维有序大孔材料(3DOM).与TiO2相比,3DOM-Bi2O3/TiO2对光的吸收至少红移60 nm,且红移至可见区.在紫外光、可见光以及微波辅助等多模式光催化降解结晶紫的实验中,复合材料3DOM-Bi2O3/TiO2表现出良好的光催化活性,其活性明显高于P25、Bi2O3和Bi2O3/TiO2.同时,该复合材料针对不同类型的染料均表现出较好的紫外光降解效果,且3次循环实验后,依旧保持较高活性.     

掺杂Fe2O3对吸附相反应技术制备TiO2的形貌和光催化性能的影响

利用吸附相反应技术制备得到了掺杂不同浓度的Fe₂O₃的TiO₂复合光催化剂。通过透射电子显微镜(TEM)、紫外可见光谱和X射线衍射(XRD)研究不同掺杂浓度对TiO₂形貌和结晶过程的影响,并利用3种波长光源下的甲基橙光降解实验考评了各个复合光催化剂的催化活性。结果表明,掺杂后复合光催化剂中Fe₂O₃分散性较好较均匀。在TiO₂紫外可见吸收光谱中由于Fe₂O₃的掺杂而出现了红移,而且随着掺杂浓度增加红移越来越明显,复合光催化剂的禁带宽度也越来越小。在焙烧过程中无定形Fe₂O₃或Fe³⁺进入了TiO₂的晶格结构,从而抑制了TiO₂的结晶过程。半导体禁带宽度的减少以及TiO₂结晶过程的抑制作用,都导致紫外光下复合光催化剂催化活性的降低。但Fe₂O₃的掺杂也使得复合光催化剂在可见光区出现了一定的光催化活性。     

Ho3+/Yb3+共掺ZnO-Al2O3-GeO2-SiO2玻璃陶瓷的制备和上转换发光性质

综合ZnO-Al₂O₃-SiO₂系和锗酸盐玻璃陶瓷的优点,采用熔融-晶化法首次制备了Ho³⁺/Yb³⁺共掺以ZnAl₂O₄为主晶相的ZnO-Al₂O₃-GeO₂-SiO₂系玻璃陶瓷。因[GeO₄]四面体和[SiO₄]四面体都是玻璃网络形成体,讨论了GeO₂取代SiO₂对玻璃陶瓷样品硬度及发光性能的影响,最终确定GeO₂的取代量为10.55%（w/w）时,玻璃陶瓷综合性能最佳。在980 nm泵浦光的激发下,发现强的绿色（546 nm）和弱的红色（650 nm）上转换发光,并研究了不同Ho³⁺/Yb³⁺掺杂比对样品上转换发光的影响,最终结果表明当Ho³⁺/Yb³⁺掺杂比为1：11（n/n）时样品荧光强度最强,在绿色上转换发光材料方面具有潜在的应用。     

Synthesis, structure and magnetic properties of new phosphates K2Mn0.5Ti1.5(PO4)3 and K2Co0.5Ti1.5(PO4)3 with the langbeinite structure

New complex phosphates of the general formula K₂M_0.5Ti_1.5(PO₄)₃ (M=Mn, Co) have been obtained from the melting mixture of KPO₃, K₄P₂O₇, TiO₂ and CoCO₃·mCo(OH)₂ or Mn(H₂PO₄)₂ by means of a flux technique. The synthesized phosphates have been characterized by the single-crystal X-ray diffraction and the FTIR-spectroscopy. The compounds crystallize in the cubic system with the space group P2₁3 and cell parameters a=9.9030(14) Å for K₂Mn_0.5Ti_1.5(PO₄)₃ and a=9.8445(12) Å for K₂Co_0.5Ti_1.5(PO₄)₃. Both phosphates are isostructural with the langbeinite mineral and contain four formula unit K₂M_0.5Ti_1.5(PO₄)₃ per unit cell. The structure can be described using [M₂(PO₄)₃] framework composed of two [MO₆] octahedra interlinked via three [PO₄] tetrahedra. The Curie-Weiss-type behavior is observed in the magnetic susceptibility.     

Self-powdering and nonlinear optical domain structures in ferroelastic β′-Gd2(MoO4)3 crystals formed in glass

Ferroelastic β′-Gd₂(MoO₄)₃, (GMO), crystals are formed through the crystallization of 21.25Gd₂O₃–63.75MoO₃–15B₂O₃ glass (mol%), and two scientific curious phenomena are observed. (1) GMO crystals formed in the crystallization break into small pieces with a triangular prism or pyramid shape having a length of 50–500 μm spontaneously during the crystallizations in the inside of an electric furnace, not during the cooling in air after the crystallization. This phenomenon is called “self-powdering phenomenon during crystallization” in this paper. (2) Each self-powdered GMO crystal grain shows a periodic domain structure with different refractive indices, and a spatially periodic second harmonic generation (SHG) depending on the domain structure is observed. It is proposed from polarized micro-Raman scattering spectra and the azimuthal dependence of second harmonic intensities that GMO crystals are oriented in each crystal grain and the orientation of (MoO₄)²⁻ tetrahedra in GMO crystals changes periodically due to spontaneous strains in ferroelastic GMO crystals.     

超声化学法制备不同形貌的CaF2微米晶

采用超声化学法,以CaCl2与不同氟源(NaBF4、K2SiF6)在溶液中反应,制得了不同形貌的CaF2微米晶(立方体、花状、多面体)。用XRD、SEM及TEM对产物晶相及形貌进行了表征。XRD结果显示所有产物均为结晶良好的立方相CaF2。SEM及TEM结果表明由NaBF4制得的产物形貌为均匀的立方体微米晶,而由K2SiF6制得的产物为多面体。在添加配体Na2EDTA的情况下,由NaBF4得到的产物为纳米片组成的花状结构。本文详细讨论了氟源种类、反应物比例、配体等反应参数对产物CaF2形貌的影响,并提出了可能的反应机理。     

The study of Bi3B5O12: synthesis, crystal structure and thermal expansion of oxoborate Bi3B5O12

The paper presents a new data on the crystal structure, thermal expansion and IR spectra of Bi₃B₅O₁₂. The Bi₃B₅O₁₂ single crystals were grown from the melt of the same stoichiometry by Czochralski technique. The crystal structure of Bi₃B₅O₁₂ was refined in anisotropic approximation using single-crystal X-ray diffraction data. It is orthorhombic, Pnma, a=6.530(4), b=7.726(5), c=18.578(5) Å, V=937.2(5) Å³, Z=4, R=3.45%. Bi³⁺ atoms have irregular coordination polyhedra, Bi(1)O₆ (d(B-O)=2.09-2.75 Å) and Bi(2)O₇ (d(B-O)=2.108-2.804 Å). Taking into account the shortest bonds only, these polyhedra are considered here as trigonal Bi(1)O₃ (2.09-2.20 Å) and tetragonal Bi(2)O₄ (2.108-2.331 Å) irregular pyramids with Bi atoms in the tops of both pyramids. The BiO₄ polyhedra form zigzag chains along b-axis. These chains alternate with isolated anions [B₂^IVB₃^IIIO₁₁]⁷⁻ through the common oxygen atoms to form thick layers extended in ab plane. A perfect cleavage of the compound corresponds to these layers and an imperfect one is parallel to the Bi-O chains. The Bi₃B₅O₁₂ thermal expansion is sharply anisotropic (α₁₁≈α₂₂=12, α₃₃=3×10⁻⁶ °C⁻¹) likely due to a straightening of the flexible zigzag chains along b-axis and decreasing of their zigzag along c-axis. Thus the properties like cleavage and thermal expansion correlate to these chains.