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53 巻 , 1 号
選択された号の論文の22件中1~22を表示しています
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特集 鉱物結晶学の多様化:新たな広がりと挑戦
1.高圧鉱物(地球深部物質)
2.地球表層鉱物(地圏物質)
  • 木原 國昭, 奥寺 浩樹
    53 巻 (2011) 1 号 p. 30-35
    公開日: 2011/04/01
    ジャーナル フリー
    A structural approach was attempted to estimate rigid ion contributions to pyroelectric coefficients, employing atomic position vectors determined in the least-squares refinement of a polar mineral, cancrinite. The two sets of positions, obtained from the centers of gravity (centroids) and modes of asymmetric probability density functions (pdf) of atoms, were applied to calculate electric polarizations, whose temperature derivatives may correspond to the rigid ion contributions to the pyroelectric coefficient, γ(σ), normally measured under the condition of constant stresses and to the secondary pyroelectric coefficients, γ(2), respectively. The primary pyroelectric coefficient γ(ε) was given as the difference γ(σ)-γ(2).
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  • 三宅 亮, 大井 修吾
    53 巻 (2011) 1 号 p. 36-41
    公開日: 2011/04/01
    ジャーナル フリー
    An isosymmetric phase transition from orthopyroxene to a new high-temperature orthorhombic phase was observed by molecular dynamics simulations for the Mg end-member composition of pyroxene (enstatite : Mg2Si2O6) and by high-temperature synchrotron X-ray powder diffraction experiments for the composition of (Ca0.06Mg1.94)Si2O6. This new phase has the same space group as orthoenstatite, Pbca. The discontinuous changes of the cell volume and cell parameters during the transition indicate a first-order transition. The transition is characterized by the switching of bonds between Mg atoms at the M2 sites and the coordinated O3 atoms. This high-temperature phase is thermodynamically distinct from the low-temperature phase, i.e., orthoenstatite in the Mg-rich portion of Mg2Si2O6 - CaMgSi2O6(diopside) phase diagram.
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  • 大川 真紀雄
    53 巻 (2011) 1 号 p. 42-45
    公開日: 2011/04/01
    ジャーナル フリー
    Vesuvianites are classified into three types, P4/nnc, P4/n, and P4nc. These varieties are interpreted as “rod polytypism”. A rare type of high-temperature skarn is developed in Kushiro (Tojyo, Shobara Hiroshima) southwestern Japan. Vesuvianites formed by the retrograde metamorphism of gehlenite, and several structural types were found corresponding to various stages of the metamorphism. The crystal structure of a unique type of vesuvianite with the space group P4/n [a=15.576 (2), c=11.835 (2) Å] is determined by single-crystal X-ray diffraction. Significant vacancies (29%) occur only on one of the two pseudo-equivalent Z1 sites (Z1b).
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  • 大藤 弘明
    53 巻 (2011) 1 号 p. 46-51
    公開日: 2011/04/01
    ジャーナル フリー
    The 3D packing structures of the microcrystals in framboidal pyrite have been studied through morphological examinations and crystallographic orientation analysis to understand the self-organization process. The structures are divided into (i) face-centered cubic, (ii) icosahedral and (iii) random packings. The detailed crystallography of pyrite framboids is characterized by high-angle (∼90°) misorientations shown by about a half of the microcrystals in a framboid. This means that the crystallographic orientation of microcrystals is not uniform even in highly ordered framboids, suggesting that their self-organization process is not crystallographically controlled, but occurs by the physical rotation of individual microcrystals.
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  • 小暮 敏博
    53 巻 (2011) 1 号 p. 52-57
    公開日: 2011/04/01
    ジャーナル フリー
    Stacking disorder is a common phenomenon in phyllosilicates but difficult to be understood using conventional diffraction techniques. In contrast, recent investigations using high-resolution transmission electron microscopy (HRTEM) have elucidated the nature of stacking disorder in various phyllosilicates, by directly observing individual layers and stacking sequences. Furthermore, simulations of X-ray or electron diffraction patterns using the information from the HRTEM results can complement the limited analysis area in TEM and quantify the degree of the stacking disorder. In this review, several examples of such analyses to reveal the stacking disorder in natural phyllosilicates are described.
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  • 宮脇 律郎
    53 巻 (2011) 1 号 p. 58-63
    公開日: 2011/04/01
    ジャーナル フリー
    A mineral substance is defined as a naturally occurring solid that has been formed by geological processes, either on earth or in extraterrestrial bodies by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (CNMMC-IMA). A mineral species is defined with the chemical composition and crystallographic properties. So far approximate 4,300 mineral species have been endorsed and approved by the CNMMC-IMA. The crystal structure is the fundamental key of the crystallography in the description of mineral. Owing to the recent developments in the hardware and software for crystal structure analysis, many of new mineral species have been described with data of crystal structures. Minor differences in atomic arrangement such as chemical orderings provide the information on the genesis of mineral.
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3.宇宙鉱物(地球外物質)
4.都市鉱物(材料科学)
  • 福田 功一郎
    53 巻 (2011) 1 号 p. 81-85
    公開日: 2011/04/01
    ジャーナル フリー
    Microtextures of belite induced by polymorphic phase transitions and a remelting reaction have been reviewed, together with the melt differentiation reaction of interstitial melt. In the α-to-α'H phase transition, the α'H-phase nucleates as lamellae within the parent α-phase so as to realize a good lattice matching across the interface. The remelting reaction, in which the α-phase belite decomposes into a liquid and the α'H-phase during cooling, is necessarily preceded by the α-to-α'H phase transition. The lamella boundaries provide heterogeneous nucleation sites for the exsolving liquid. A variety of microtextures results depending on the surface tension between belite lamellae and exsolved liquid as well as on the cooling rate. As the simultaneous crystallization of zoned ferrite and belite proceeds during the cooling process of clinkers, the coexisting melt progressively increases the Al2O3/Fe2O3 ratio. After the termination of the ferrite crystallization, the aluminete and belite crystallize out of the differentiated melt.
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  • 奥寺 浩樹, 鱒渕 友治, 吉川 信一
    53 巻 (2011) 1 号 p. 86-90
    公開日: 2011/04/01
    ジャーナル フリー
    Apatite-type RE9.33(SiO4)6O2 rare-earth silicate compounds are of great interest for their oxide ion conductivity at moderate temperatures. Crystallographic space group and structural parameters of La/Nd9.33(SiO4)6O2 were investigated based on single-crystal X-ray diffraction data at room temperature for La9.33(SiO4)6O2 and at various temperatures from 150 to 900 K for Nd9.33(SiO4)6O2. Based on the most accurate diffraction data to date, these compounds have an apatite prototype structure (space group P63/m) with no symmetry lowering, site splitting nor interstitial oxide ion in the structure. Most striking feature of the structure is large anisotropy in thermal motions of the oxide ion at the anion channel site. Even at room temperature, the mean-square displacement of the channel oxide ion in La9.33(SiO4)6O2 is 16 times larger in [001] than those normal to the direction. Not striking but important point is that there is no sign of interstitial oxide ion which had been proposed as a charge carrier in La9.33(SiO4)6O2 and related compounds. These findings imply straight migration of oxide ion inside the channel as a primary mechanism of oxide-ion conductivity in these compounds. Size and shape of the anion channel might be a key to achieve high oxide-ion conductivity in these compounds.
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