Showing papers by "Sumio Sakka published in 1991"

Structure of PbOBi2O3Ga2O3 glasses

Abstract: The structure of PbOBiO1.5GaO1.5 glasses has been investigated by IR and Raman spectroscopy. An infrared absorption band involving four-coordinated Ga3+ ions was observed at about 610–650 cm−1. The peak of this band shifts toward higher wavenumbers with increasing GaO1.5 content, indicating that covalency of GaO bond increases with increasing GaO1.5 content. The peak deconvolution was made on Raman spectra of the glasses. The Raman bands at about 130 cm−1, 400 cm−1, 550 cm−1 and 650 cm−1, obtained by deconvolution, have been assigned to PbO or BiO, GaOPb or GaOBi, GaOGa, and GaOnon-bridging vibrations, respectively. The presence of 550 cm−1- and 650 cm−1-band indicates that Ga3+ ions are coordinated by four oxygens. The much higher peak wavenumber of the 550 cm−1-band in the spectrum of BiO1.5GaO1.5 glass compared with that in the spectrum of PbOGaO1.5 glass is attributed to the much higher ionic field strength of Bi3+ ion compared with that of Pb2+ ion. The fraction of non-bridging oxygens in GaO4 tetrahedra decreases with increasing PbO and BiO1.5 contents. It is assumed that most Pb2+ and Bi3+ ions are network formers.

Preparation of lithium aluminosilicate glass-ceramic monolith from metal alkoxide solution

Abstract: Glass-ceramic monoliths with a composition of Li2O·Al2O3·4SiO2 have been synthesized by the sol-gel technique using metal alkoxides as starting materials. Heating dried gel monoliths of about 36 mm diameter and height to appropriate temperatures gave glass-ceramic monoliths of about 20 mm diameter and height without the occurrence of cracks, while a melt-derived glass body of the same composition was cracked or softened on heating. The glass-ceramic monoliths obtained by heating gel monoliths at 1000 ‡C for 40 h were a porous body, whose bulk density and porosity were 1.62 g cm−3 and 34%, respectively. On heating gel monoliths, Β-eucryptite crystals were first precipitated around 750 ‡C, followed by precipitation of Β-spodumene crystals at 830 ‡C. At higher temperatures the latter grew at the expense of the former phase. The crystallized specimens exhibited very low thermal expansion coefficient ranging from −13-12×10−7 ‡C−1 at temperatures from room temperature to 700 ‡C depending on the heat-treatment temperature of gels, indicating that a porous glass-ceramic monolith with ultra-low thermal expansion can be prepared using the present sol-gel method.

Preparation of Li2B4O7 Films with Preferential Orientation by Sol–Gel Method

Abstract: Li2B4O7 films, a promising material for surface acoustic wave devices, were prepared by the sol—gel method using metal alkoxide precursors as starting materials. The Li2B4O7 films on silicon (100) and (111) single crystals prepared from a coating solution to which acetic or hydrochloric acid was added were highly oriented along the (122) plane, whereas those without acid additive were randomly oriented. The results were interpreted based on the basic sol-gel chemistry and the lattice matching between the film and substrate.

Structure of na2o.2tio2 glass

Abstract: X-ray radial distribution analysis and Raman spectroscopic measurement were carried out on Na2O-2TiO2 glass prepared by twin-roller quenching method. It is found that four-coordinated Ti4+ ions may be predominant over six-coordinated ones in the present glass. It is also found that the fraction of six-coordinated Ti4+ ions is larger in the present glass than in K2O·2TiO2 and Cs2O·2TiO2 glasses. Poorer glass-forming ability of the Na2O-TiO2 system compared with the K2O-TiO2 and Cs2O-TiO2 systems is ascribed to a larger fraction of TiO6 octahedron for the former system.

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosillcate Glasses in Copper‐Containing Molten Salt: I, Monovalent Copper Salt, CuCl

Abstract: Cu+⇌ R+ (R = Li, Na, and K) ion exchange experiments were conducted for 20R2O·10Al2O3·70SiO2 glasses in molten CuCl at 550°C in air and nitrogen atmospheres. The depth profiles of the copper incorporated into glasses were determined with an electron microprobe X-ray analyzer. The total amount of diffusing copper, Mt, strongly depended on the type of alkali ion in the glass and the ion-exchange atmosphere; i.e., Mt increased with increasing cationic size in the order Li < Na < K and Mt was greater in air than in nitrogen. The Cu ⇌ R+ ion exchange kinetics are discussed in detail.

Copper ⇌ Alkali Ion Exchange of Alkali Aluminosilicate Glasses in Copper-Containing Molten Salt: II, Divalent Copper Salts, CuCl2 and CuSO4

Abstract: The ion-exchange mechanism between copper and alkali ions, when 20R2O · 10Al2O3· 70SiO2 (R = Li, Na, and K) glasses are immersed in divalent copper-containing molten salts in air and nitrogen at 550°C, has been investigated. In molten CuCl2, the ion-exchange behavior in both air and nitrogen was very close to that in molten CuCl in air reported previously. This is explained by assuming that CuCl2 decomposes into CuCl and Cl2 at 550°C and the Cu+ ions thus formed mainly diffuse in glasses to replace alkali ions, where Cl2 acts as an oxidizing agent just like oxygen. In the case of molten CuSO4─2SO4, a small amount of Cu+ which is present in the molten state plays a primary role in the Cu ⇌ R+ ion exchange process, although the contribution of direct Cu2+⇌ 2R+ ion exchange cannot be ignored.

Properties of oxybromide tellurite glasses in the system LiBrLi2OTeO2

Abstract: The glass transition temperature, thermal expansion coefficient and electrical conductivity have been measured for oxybromide tellurite glasses in the system LiBrLi2OTeO2. Results are discussed in relation to the glass structure together with the previous results reported of the LiClLi2OTeO2 system. The glass transition temperature is higher and the thermal expansion coefficient is lower in the LiBr-containing glasses than in corresponding LiCl glasses. The electrical conductivity is lower in the LiBr-containing glasses especially in glasses with low TeO2 content. These phenomena are explained by considering the strength of the TeOax bond, where ax denotes an axial position, and the amount of TeO32−; the degree of weakening of the TeOax bond, which brings about the formation of TeO32−, is smaller in LiBr glasses than in the LiCl glasses. In glasses with high TeO2 content, increase of the LiBr/(LiBr+Li2O) ratio increases the glass transition temperature and decreases the thermal expansion coefficient. This is explained in terms of the variation of strength of the TeOax bond.

Ammonolysis of silica gels containing methyl groups

Abstract: Silica gels containing a constant concentration of methyl groups directly bonded to silicon atoms have been prepared from methyltriethoxysilane (MTES) and mixtures of tetraethylorthosilicate (TEOS) with dimethyldiethoxysilane (DMDES) and hexamethyldisiloxane (HMDS) These gels were subsequently ammonolyzed The temperature range in which significant nitrogen is incorporated into a gel lies between 600 ° C and 800 ° C for the gel derived from MTES, between 800 ° C and 1000 ° C in the gel derived from DMDES with TEOS and at 1000 ° C in the gel derived from HMDS with TEOS Three different nitridation processes operate depending on the temperature The processes are reaction of ammonia with (i) methyl groups bonded to silicon atoms, (ii) SiOH groups and (iii) SiOSi bonds The low-temperature process is dominant in MTES-derived gel and the middle- and high-temperature processes are dominant in DMDES- and HMDS-derived gels The nitridation processes depend on the amount of SiOH groups in the gel, the thermal stability of methyl groups present and the reactivity of the gel with SiOH or SiNH 2 groups to form SiOSi, SiNHSi or nitride bonds

Preparation of Lead-Based Perovskite Films by Sol-Gel Method and Their Properties : Thin Films

Abstract: Ferroelectric Pb(Fe0.5Nb0.5)O3(PFN)-PbTiO3(PT) thin films have been prepared on silica glass and silicon single crystal substrates by the sol-gel method using lead acetate, iron nitrate, niobium ethoxide and titanium tetraisopropoxide as precursors. It has been found that 38 mol% excess lead must be added to a starting solution to obtain single phase perovskite PFN coating films, while single phase perovskite 0.2PFN·0.8PT coating films can be prepared from the corresponding stoichiometric starting solution. The coating film shows a dielectric constant of about 500-1100 and dielectric loss of about 0.06-0.18 at 1000 Hz.

Preparation of Lead-Based Perovskite Films by Sol-Gel Method and Their Properties

Abstract: Ferroelectric Pb(Fe0.5Nb0.5)O3(PFN)-PbTiO3(PT) thin films have been prepared on silica glass and silicon single crystal substrates by the sol-gel method using lead acetate, iron nitrate, niobium ethoxide and titanium tetraisopropoxide as precursors. It has been found that 38 mol% excess lead must be added to a starting solution to obtain single phase perovskite PFN coating films, while single phase perovskite 0.2PFN·0.8PT coating films can be prepared from the corresponding stoichiometric starting solution. The coating film shows a dielectric constant of about 500-1100 and dielectric loss of about 0.06-0.18 at 1000 Hz.

Structural study of TeO 2 and LiCl-Li 2 O 2 -TeO 2 glasses by Raman and 125 Te MAS NMR spectroscopies

Abstract: The structures of TeO2 and Li2O-LiCl-TeO2 glasses have been investigated by means of Raman and 125Te MAS NMR spectroscopy. Extremely large isotropic chemical shifts of 1500–1700 ppm and linewidths of 160–230 kHz were observed in the 125Te MAS NMR spectra of both TeO2 crystals and TeO2-based glasses, indicating that Te atoms in TeO4 or TeO3+1 polyhedra in oxide crystals and glasses have very low symmetry mainly due to the presence of a lone pair of electrons. The Raman spectra revealed that pure TeO2 glass has a network structure similar to that of α-TeO2 rather than β-TeO2. The present Raman and 125Te MAS NMR spectra also confirmed that not only Li2O but also LiCl modifies the TeO2 glass network, forming TeO3, trigonal pyramid.

Sol-Gel Method and Its Applications

Abstract: ゾル-ゲ ル法1)~4)は溶液か ら低 温で各種 の材料 を合成 する方法で,現 在,先 端材料分野で広 く注 目を集 めて い る.こ の方法で は,主 として金属の アルコキシ ド,ア セ チルアセ トナ ト,カ ルボ ン酸塩の ような金属有機化合物 や金属硝酸塩の ような無機化合物の溶液 をつ くり,こ れ らの化合物の加水分解重 合によって分子 クラス ターや微 細 な粒子の分散 した ゾルに変 え,さ らに反応 を進 ませて ゲル とす る。ゲル として固化する際に,バ ルク(板 やロ ッ ド),繊 維,コ ーテ ィング膜の よ うな形 をもつ材料 につ くりあげ るのが ゾル-ゲル法の特徴であ るが,粉 末 ある いは粒体 として利用するこ ともある。 また,ゲ ルの状態 で使用 する材料利用法が しだいに新材料の合成法 として 盛んにな りつつある.し か し形 のある ゲル を加熱 して形 のある ガラス またはセ ラ ミックスをつ くる ことはゾルゲル法 の最 も重要な応用分野 である. ゾル-ゲ ル法 では,バ ル ク,繊 維,コ ー ティング膜 を 直接つ くる場合 も,ゾ ル-ゲ ル法でつ くった粉末 を焼結 原料 として使用する場合 も,結 晶性の酸化物や炭酸塩 の 原料 を利用する従来の方法に くらべて数百 °C ~1000°C も低い温度 で目的物 をつ くる ことがで きる.こ のため,' 従来の方法 ではで きない化合物 を新 しく合成する ことが で きる.ま た,従 来の方法ではで きない形状の材料,た とえば,セ ラ ミックスの繊維 やコーテ ィング膜 を比較的 容易につ くるこ とがで きる.さ らに,場 合 によっては高 い生産性 を期待す ることがで きる. 本報告では,ゾ ル-ゲ ル法の概略 を示 し,バ ルク,繊 維, コー テ ィング膜 の直接 合成 について述べ る。 と くに ゾ ル-ゲ ル法の コーテ ィング膜作製へ の応用 について詳 し く解説する.

Preparation of Li2B4O7 Films with Preferential Orientation by Sol-Gel Method.

Abstract: Li2B4O7 films, a promising material for surface acoustic wave devices, were prepared by the sol—gel method using metal alkoxide precursors as starting materials. The Li2B4O7 films on silicon (100) and (111) single crystals prepared from a coating solution to which acetic or hydrochloric acid was added were highly oriented along the (122) plane, whereas those without acid additive were randomly oriented. The results were interpreted based on the basic sol-gel chemistry and the lattice matching between the film and substrate.