Research Themes

• Float zone growth of high-quality Yb-doped oxide single crystals and their application to ultra-short pulse lasers
  Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
  Apr. 2017 - Mar. 2020
  Higuchi Mikio
  For the application to ultrashort pulse laser, Yb-doped oxide single crystals were grown by the floating zone melting method and their optical properties were investigated. For a K2NiF4 type crystal Yb:CaYAlO4, a congruent melting composition that is slightly different from the stoichiometric composition was revealed, and high quality crystals without macroscopic defects using the congruent composition. Continuous wave laser oscillation using this crystal was successfully performed. It was found that the melilite type Yb:CaGdAl3O7, which has better emission characteristics than the K2NiF4 type, melts incongruently. In order to solve this problem, a double-pass traveling solvent floating zone melting method was newly developed and crystals having the target composition were successfully grown from the initial grown part.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 17K06010
• Development of hydrooxide ion-conductive layred double hydroxides with electron and light functions
  Grants-in-Aid for Scientific Research
  01 Apr. 2013 - 31 Mar. 2016
  Tadanaga Kiyoharu, HIGUCHI MIKIO
  Zn-Al layered double hydroxide (LDH) thin films intercalated with Eosin Y were prepared by the sol-gel method with hot water treatment. The heat-treated Zn-Al Eosin-Y LDH thin film was confirmed to work as the electrode of a solar cell under visible light irradiation. Powders of Zn-Al layered LDHs intercalated with eosin Y were also found to show the photocatalytic activity under visible light irradiation.
  The ionic conductivity of (Ni, Mn)-Al LDHs and (Ni, Mn)-Fe LDHs intercalated with CO32- was found to be higher than that of Ni-Al LDH or Ni-Fe LDH. The addition of LDHs to the catalyst layer of an air-electrode increased the current for oxygen reduction reaction (ORR). H2-O2 fuel cells with Mg-Al LDHs as an electrolyte were confirmed to be operated.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 25289230
• Development of novel Nd-doped vanadate single crystals for ultra-short pulse lasers
  Grants-in-Aid for Scientific Research
  2009 - 2011
  HIGUCHI Mikio, WADA Satoshi
  Novel single crystals of Nd : LaVO4 were grown by the floating zone method and their spectral properties were investigated aiming for development of an ultra-short pulse laser system using a laser diode as a pumping source. The crystals were grown along Z-axis, which is one of the optical elasticity axes, and they were of optically high quality without any macroscopic defects. The absorption and emission spectra showed unusually broadened peaks as a Nd-doped crystals, and their optical aisotropy along each elasticity axis is not significant. When single-mode oscillation was examined, a high slope efficiency of 76 %, which is close to theoretical one, was obtained. A broadened laser spectrum of 14 nm was obtained by multi-mode oscillation, and it is accordingly possible to achieve an ultra-short pulse less than 300 femtosecond.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 21350111
• Development of novel Nd-doped vanadate single crystals forLD-pumped ultra-short pulse lasers
  Grants-in-Aid for Scientific Research
  2007 - 2008
  HIGUCHI Mikio, WADA Satoshi
  半導体レーザ(LD)励起可能な超短パルスレーザシステムの構築を目指して、新規バナデイトNd : Ca_9La(VO_4)_7およびNd : Ca_2La_<0.67>(VO_4)_2単結晶の育成をおこない、その分光学的性質を調査した。両者ともに大気雰囲気下での育成により、部分的にではあるが、比較的良質な結晶が得られた。これらの結晶は幅の広い吸収帯ならびに発光帯を有しており、LD励起フェムト秒レーザ材料として有望であることがわかった。
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 19550188
• 一方向凝固による希土類酸化物含有共晶体のパノスコピック形態制御とその光学特性
  科学研究費助成事業
  2005 - 2006
  高橋 順一, 樋口 幹雄
  微細な口径を有するファイバーの光学結晶が互いに接触することなく平行にマトリックス中に埋め込まれた組織をもつ凝固体は、異方性発光や光の閉じ込め効果など、バルク結晶にはない新しい機能を付与した光学素子としての応用が期待される。本研究では、溶媒移動浮遊帯域溶融法により、希土類元素を含む種々の酸化物共晶系について、任意組成の一方向凝固体を作製してきた。今年度は、昨年度において良好な組織が得られたGdAlO_3-Al_2O_3系に加えて、REAlO_3-MgAl_2O_4系について、組成および成長条件と得られた組織との関係を検討した。
  GdAIO_3-A12O_3系においてGdAlO_3含有量が40mol%の場合、目的とする組織が横断面、縦断面いずれにも観察された。GdAlO_3を35mol%としても同様の組織が観察されたが、A12O_3相が独立して大きな組織を形成している部分も存在するようになった。フアイバー状GdAlO_3相の径は成長速度の低下に伴い増大し、50mm/hおよび20mm/hではそれぞれ約1μmおよび2μmとなった。現段階では試料全体を目的とする組織とするには至っていないが、成長初期にネッキングをおこなうとマトリックス相であるAl_2O_3粒子の数が淘汰され、目的とする組織の体積分率は60-70%に増大することが明らかとなった。
  REAlO_3-MgAl_2O_4系については、独立したREAIO_3相の形態がGdAlO_3-Al_2O_3系のものと異なり、ほぼ三角形の断面形状をもっているとともに、希土類元素のイオン半径が減少するにつれて角の丸い形からより明瞭な三角形へと変化した。縦断面の観察ではLaAlO_3-MgAl_2O4系の場合のみ、ファイバー状の組織が観察されたが、REがY、GdおよびLuの場合には、REAIO_3相は三角錐状になっていることが確認された。
  日本学術振興会, 特定領域研究, 北海道大学, 17042004
• Float zone growth of rare-earth doped lutetium orthovanadate single crystals as new solid state laser materials
  Grants-in-Aid for Scientific Research
  2003 - 2004
  HIGUCHI Mikio, WADA Satoshi
  Neodymium-doped lutetium orthovanadate (Nd : LuVO_4) has larger absorption and emission cross sections as compared with conventional Nd-doped rare earth orthovanadates and is expected to be applied for laser-diode pumped solid state lasers. LuVO_4 is also expected to be a good host crystal for Tm and Yb, since the tonic radius of Lu^<3+> is comparable to those of Tm^<3+> and Yb^<3+>. In this study, the growth technique of rare-earth (Nd, Tm and Yb) doped LuVO_4 single crystals by the floating zone technique has been established and some spectroscopic properties as a laser material have been investigated.
  Each dopant was added with 0.5-4 at% with respect to Lu. Growth conditions were as follows : traveling rate of the molten zone was 20-40 mm/h ; rotation rate was 30-40 rpm ; direction was [110] and atmosphere was an oxygen flow Any as-grown crystal was colored in yellowish ocher, but the coloring was completely eliminated by annealing at 1000 ℃ for 20h in air. Polarizing microscopy proved that the grown crystals contained no macroscopic defects but growth striations were observed only in Nd-doped crystals. Effective segregation efficient was determined to be close to unity for Tm and Yb and about 0.5 for Nd. At this stage, single crystals 5 mm in diameter and 50 mm long have been grown reproducibly for Tm-and Yb-doping of up to 5 at% and Nd-doping of up to 1 at%.
  The absorption coefficient of Nd : LuVO_4 was 1.4 times as high as those of other rare-earth orthovanadates. The Nd : LuVO_4 (1 at%) single crystal exhibited excellent laser performance with 880 nm pumping ; that is, the slope efficiency was 73 % and the threshold was 7 mW. Although the laser oscillation experiments for Tm and Yb-doped crystals are underway, it is expected that those crystals also exhibit good laser performance on the basis of their excellent spectroscopic properties.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), HOKKAIDO UNIVERSITY, 15550169
• Float zone growth of thulium-doped rare-earth orthovanadate single crystals for eye-safe lasers
  Grants-in-Aid for Scientific Research
  2001 - 2002
  HIGUCHI Mikio, KODAIRA Kohei
  The demand for eye-safe lasers has been increasing in the field of lidar sensing and medical applications. Thulium (Tm)-doped crystals are one of the promising materials for the eye-safe lasers because they can easily be pumped usuing laser-diode. As a host crystal of the Tm-lasers, GdVO_4 single crystals are superior to other crystals such as YAG and fluorite from the viewpoints of thermal conductivity and absorption coefficient. In this study, float zone growth of Tm-doped GdVO_4 single crystals were tried and their spectroscopic properties were investigated.
  Transparent, crack-free Tm : GdVO_4 single crystals were successfully grown by the floating zone method using an pure oxygen flow as a growth atmosphere. Tm-doping of up to 20 at% was possible at a high growth rate of 20 mm/h. Growth direction contained a number of low-angle grain boundaries, which deteriorate their optical uniformity, whereas the crystals grown along the [110] direction had to low-angle grain boundaries. The necking process was also essential to enhance the optical quality. The formation of bubble inclusions was effectively suppressed by optimizing the combination of growth rates and crystal rotation rates.
  The absorption coefficient around 800 nm was large enough for pumping with a laser-diode of 808 nm which is conventionally used for Nd-lasers. Intensive emission was observed even above 1950 nm where the self-absorption could be neglected. The fluorescence decay time decreased from 2.1 to 0.5 ms with increasing Tm-concentration but is long enough for laser oscillation. Although the laser oscillation is under way, the Tm : GdVO_4 single crystals grown by the floating zone method are expected to be potential materials for 2 μm lasers.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), HOKKAIDO UNIVERSITY, 13650888
• Growth of Apatite-Type Lanthanide Silicates Single Crystals by the Floating Zone Method and Mechanism of Their Oxide Ionic Conduction
  Grants-in-Aid for Scientific Research
  1998 - 1999
  KODAIRA Kohei, NAKAYAMA Susumu, HIGUCHI Mikio
  Lanthanide silicates with an apatite structure are a new type of oxide ionic conductors; at low temperatures blow 600 ℃ the conductivities of these materials are superior to that of stabilized zirconia. However, no large-size single crystals of these materials have so far been grown, and accordingly their essential properties have not yet clarified. In this study, single crystals of apatite-type lanthanide silicates were grown by the floating zone method and their electrical properties were evaluated.
  From the viewpoint of light-absorption, praseodymium, neodymium and samarium silicates crystals were grown. All the crystals were easily grown by the floating zone method since they melt congruently. For the Nd-system, bubble inclusions were occasionally contained but the use of a Nd-poor feed rod enabled to grow an inclusion-free crystal. The congruent composition may be different form the stoichiometric one and is located at Nd-poor side. For the Sm-system, macroscopic defect-free crystals have not yet been obtained due to the formation of microcracks. Since the cracks were formed parallel to the c-plane, however, they do not hinder significantly the measurements of conductivities. For all the kinds of crystals, the conductivities parallel to the c-axis were larger by about one order of magnitude than those perpendicular to the c-axis. These results proved that the oxide ions at 2a site migrate preferentially through the channel parallel to the c-axis of the apatite structure. The conductivities of the single crystals were independent on the kinds of rare-earth ions although remarkable decrease in the conductivities were observed for the sintered compacts. This is because the oxide ions at 2a site is coordinated by three rare-earth ions at 6h site on the same plane level.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 10450327
• Growth of Fibrous Single Crystals of Oxides by the Floating Zone Method
  Grants-in-Aid for Scientific Research
  1997 - 1998
  HIGUCHI Mikio, KODAIRA Kohei
  In various optical devices, efficient laser oscillation or wavelength conversion is expected using a fiber crystal, in which laser beam is encapsulated. In this study, the floating zone method, which had been employed to grow bulk crystals, was applied to grow fiber crystals of oxides Neodymium-doped yttrium orthovanadeate (Nd : YVO_4), which has attracted the attention as a laser material with laser-diode pumping, was chosen as a model material. Growth conditions to obtain thinner crystals were examined and the relation between the crystal diameter and quality was clarified.
  To keep a stable molten zone, the feed diameter should be decreased with decreasing crystal diameters and the ratio of the feed diameter to the crystal one should be less than three. In the case of less than 1 mmphi. the ratio should be about two. To realize these conditions, a single crystalline feed rod with a uniform diameter was used by cutting and grinding after the zone pass. The minimum diameter obtained was 0.8 mm. Thinner crystals are expected by using a four-ellipsoidal type apparatus. Which has much higher convergence efficiency than in the present apparatus. A drastic decrease in dislocation density was found in the crystals below 3 mmphi, in which dislocations were spontaneously decreased with continuing crystal growth. The decrease in the thermal stresses because of the decrease in the crystal diameter would contribute to the quality improvement.
  In this study, a basic technique for growing fiber crystals of oxides by the floating zone method was established and the quality of the crystals was improved with decreasing crystal diameters. This technique is also applicable to grow other kinds of fiber crystals that were difficult to grow by the conventional methods.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), HOKKAIDO UNIVERSITY, 09650917
• 高温用セラミックフィルター作製のための組成およびポア構造傾斜プロセス
  科学研究費助成事業
  1997 - 1997
  小平 紘平, 樋口 幹雄, 高橋 順一
  コ-ジェライトは現存するセラミックスの中では最適な燃焼ガス用高温フィルター材料である。本研究では、さらなる材料強度の向上とより高温での使用を実現するために、コ-ジェライト(C)とムライト(M)との組成傾斜体の作製法の確立を目的とした。まず、コ-ジェライトおよびムライト組成の混合ゾルを仮焼し、その後のPSZボールによる微粉砕と蒸留水中への分散により噴霧に最適な懸濁液を調製した。両懸濁液を別々のノズルから高分子フォウム中へ噴霧堆積させることにより、特定の組成傾斜プロフィールをもつ2種類の組成傾斜粉体層を作製した。すなわち、試料の表側から裏側に向かって順にコ-ジェライトムライトコ-ジェライト(CMCと略記)とする試料と逆のMCM試料である。ただし、ムライトのみではコ-ジェライトが緻密になる焼成温度においては焼結しないため、ムライト側の組成は最大でM:C【approximately equal】0.7:0.3となるように調整した。1445°Cで焼成した場合、いずれの試料ともほぼ目的とする組成傾斜となっていたが、噴霧後半の部分の傾斜度において若干ズレが大きくなる傾向が現われた。これらの組成傾斜体のポア構造(気孔率および気孔径分布)はC/M比率に対応して変化し、コ-ジェライト比率の多い組成域では数ミクロンの気孔が分布しているのに対し、ムライト含有量の多い部位では多数の大きな気孔が存在した。また微細構造としては、棒状のムライト粒子群と通常の形状を有するコ-ジェライト粒子群からなり、それらの粒子群のサイズは噴霧液滴のそれと対応すると考えられた。さらにこれらの試料に対して、バーナー加熱(〜1000°C)および電気炉加熱(1200°C)後に水中急冷を行ったところ、いずれの場合も急冷後の割れは認められなく、また抗折強度の低下もなかった。したがって、本研究で作製したCMCおよびMCM試料とも優れた耐熱衝撃抵抗特性を持っていることが明ら
  日本学術振興会, 重点領域研究, 北海道大学, 09229201
• Growth of Large Rutile Single Crystal by Heater-Inserted Floating Zone Method
  Grants-in-Aid for Scientific Research
  1996 - 1997
  KODAIRA Kohei, HIGUCHI Mikio, TAKAHASHI Junichi
  Rutile single crystals have attracted much attention for their applications as polarizar. The single crystal have success fully grown by the floating zone (FZ) method, which is difficult to grow large size crystals because the molten zone is kept only by surface tension of the melt. In this study, we have grown large rutile single crystals by the heater-inserted floating zone (heater-inserted FZ) method, in which the melts were supported at the bottom of the iridium crucible and growing crystals The size of a hole at the crucible center should be 2mm in diameter to keep continuous feeding of the melt to the growth region. The use of heat insulating materials made of porous zirconia was effective to melt the rutile. A heat-shielding plate below the crucible was also effective to shallow temperature gradient.Continuous feeding of raw materials were possible to grow for long time by using granular TiO_n. Rutile single crystals with about 25mm in diameter were successfully grown by the heater-inserted FZ method. It will be possible to grow rutile single crystals having larger diameters by a larger crucible.
  Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), HOKKAIDO UNIVERSITY, 08455401
• 組成およびポア構造傾斜高温セラミックフィルターの作製
  科学研究費助成事業
  1996 - 1996
  小平 紘平, 樋口 幹雄, 高橋 順一
  次世代の高効率複合発電のひとつとして、高温の燃焼ガスを用いて直接タービンを回すシステムが検討されている。このシステムにおいては、高温の燃焼ガス中の含まれている微粒子をきわめて高い効率で捕捉するためのフィルターが不可欠である。このフィルター材に対しては厳しい高温特性が要求され、現存する耐熱性材料の中ではコ-ジェライトセラミックスが最適と考えられている。しかしながら、耐久性に乏しく、まだ信頼性の高いフィルターは得られていない。本研究では、高強度化とより高温での使用が可能なフィルターとして、コ-ジェライトームライト傾斜機能材料の作製を目的とした。またこの場合、高温フィルターとして基本的に具備すべき優れた耐熱衝撃抵抗特性を低下させないように、ポア構造の傾斜化も必要である。これらの目的に対して、本研究では新たにスプレー法による作製を試みた。まず、採用したノズルのスプレーパターンを調べ、最適なスプレー距離、スプレー圧力等の条件を明確にした。スプレー用原料としては、シリカゾルとアルミナゾルをベースにして調製した混合ゾルと、それらのゾルを一度仮焼後粉砕・分散して調製した二種類の懸濁液を用いた。本年度はそれぞれコ-ジェライトとムライト組成を有する懸濁液を、別々のノズルからムライト基板上に噴霧する複スプレー法により傾斜層の形成を行った。まだスプレープロセスによる作製法を確立するまでには至っていないが、焼成体(1450°C12時間)のXRD分析の結果、混合ゾルを用いることにより、組成傾斜層が得られることが明らかになった。ただし、乾燥時の収縮・変形が大きな問題として残されており、今後さらにノズルの選択、最適な懸濁液の調製、またより実際的な材料を作製するためのフィルター全体の構造について検討を行う。
  日本学術振興会, 重点領域研究, 北海道大学, 08243201
• Studies on Growth and Characterization of High Quality Metal Oxide Single Crystals
  Grants-in-Aid for Scientific Research
  1993 - 1995
  KODAIRA Kohei, HIGUCHI Mikio, TSUCHIDA Takeshi, TAKAHASHI Junichi
  High quality metal oxide single crystals have been applied to many electronic devices. This study is to clarify the growth and characterization of rutile and trirutile single crystals by floating zone method, and also quartz single crystals by hydrothermal method. Following results were obtained through this investigation.
  (1) Rutile single crystals free from low-angle grain boundaries were grown with the addition of Al, Zr and Sc. Optical quality of the crystals was superior to that of commercially available crystals grown by the Verneuil method.
  (2) MgTa_2O_6 single crystals which has trirutile structure were successfully grown by FZ method. The refractive indices for ordinary and extraordinary rays were 2.07 and 2.18 under white light, respectively, and birefringence was 0.11. Pale green NiTa_2O_6 single crystals were also grown by the same method. The crystals had strong absorption spectra in the wave length ranges of 300-500,650-900 and 1100-1600 nm.
  (3) Quartz single crystals were grown from ammonium fluoride solutions at 230-280 ﾟC and 4-100 MPa under hydrothermal condition. The maximum growth rate of the Z face attained 0.88 mm/day which was comparable to that in alkaline solutions. The linear defect density in Z growth zone was about 10^3-10^5 pcs/cm^2, higher than that alkaline solutions. Strong absorption at about 3500cm^<-1> by -OH streching vibration was observed in FTIR spectra.
  Japan Society for the Promotion of Science, Grant-in-Aid for General Scientific Research (A), HOKKAIDO UNIVERSITY, 05403023
• Studies on preparation of transparent conductive oxide thin films by sol-gel method
  Grants-in-Aid for Scientific Research
  1990 - 1991
  KODAIRA Kohei, FURUSAKI Tsuyoshi, HIGUCHI Mikio
  Sn-doped In_2O_3 and Sb-doped SnO_2 thin films with 140 nm in thickness prepared on fused silica substrates by a sol-gel method. The transmittance of these films was 90% in the visible region. The interaction between the film and a fused silica substrate was not recognized by firing above 55ﾟC for 30minutes.
  In_2O_3 thin films crystallized above 350ﾟC, after OH groups were dehydrated during the firing. The minimum resistivity (3X10^<-3>OMEGAcm) was attained for the film with 7mol%Sn prepared at 850ﾟC for 30 minutes. After the film was annealed at 300ﾟC for 30 minutes in vacuum, the resistivity of the film decreased to 7X10^<-4>OMEGAcm.
  SnO_2 thin films progressively crystallized above 550ﾟC, after OH groups were dehydrated during the firing. Grain growth of primary particles in the films proceeded with raising up firing temprature and also without any substantial change in the porosity. The minimum resistivity (3X10^<-3>OMEGAcm) was attained for the film with 7.5mol%Sb prepared at 800ﾟC for 30 minutes.
  Japan Society for the Promotion of Science, Grant-in-Aid for Developmental Scientific Research (B), Hokkaido University, 02555158
• Preparation of High Purity Nitrides
  Grants-in-Aid for Scientific Research
  1989 - 1990
  KODAIRA Kohei, FURUSAKI Tsuyoshi, HIGUCHI Mikio
  AlN ceramics have a high thermal conductivity and low thermal expansion. There are so many applications to structural materials as LSI substrates. The purpose of this work is to establish preparation procedures of AlN fine powder with high purity by direct nitridation of aluminum metal. The nitridation of Al-powder was conducted under a stream of nitrogen. Relatively rapid nitridation reaction began at temperature range of 850^ﾟC to 1200^ﾟC. The powders prepared at 900^ﾟC for 2 hours were identified as AlN with a small amounts of residual metallic Al by powder X-ray analysis. Nitridation of aluminum by an addition of 30wt% AlN powder was very useful for the production of well dispersed powders without aggregation. AlN fine powders showing with color were obtained by re-nitridation at 1600 ^ﾟC of the powder prepared at 900 ^ﾟC for 2 hours. Two stage niidation of aluminum with AlN powders is very advantageous method for the preparation of fine powder with high sintering properties.
  Japan Society for the Promotion of Science, Grant-in-Aid for General Scientific Research (B), Hokkaido University, 01470066
• High Pressure Hydroghermal Growth of Beryl Single Crystals
  Grants-in-Aid for Scientific Research
  1986 - 1987
  KODAIRA Kohei, HIGUCHI Mikio, SHIMADA Shiro
  Beryl crystals were grown from nonequilibrium state by dissolution-precipitation of each starting powders.Under high pressure hydrothermal conditions,crystal growth was observed at 500゜ー650゜C and 0.1-0.3N NaOH solutions.Clear and smooth beryl crystals were grown from the most suitable condition at 600゜C and 0.1N NaOH solution.Representative P(101^^-1)face for hydrothermal growth was developed.The P(101^^-1)fece seems to have relatively high growth rate comparing with that of other m(101^^-1)and c(0001) faces.
  In the IR spectra of the beryl crystals obtained from 0.1-0.3N NaOH solutions, two sharp stretch at 3690 and 3580 cm^<-1> were observed.There are large differences in the IR spectra of synthetic hydrothermal emeralds and that investigated by the present beryl,both of which show a sharp OH stretch band at 3690 cm^<-1>. In addition this band, high pressure hydrothermal beryl exhibits a sharp band at 3580 cm^<-1>,Hich is the same as the natural Colombian emerald.The high pressure hybrothermal beryl can not be distinguished with natural ones.The channel was also somewhat large for the direction of a-axis in the present beryl comparing with the emeralds grown by flux method on account of alkali cations and wster.The refractive index and densities were clearly large so as to be in natural emeralds.
  Japan Society for the Promotion of Science, Grant-in-Aid for General Scientific Research (B), Hokkaido University, 61470066