Netsu Sokutei
Online ISSN : 1884-1899
Print ISSN : 0386-2615
ISSN-L : 0386-2615
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Volume 25, Issue 5
Displaying 1-3 of 3 articles from this issue
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  • Phase Transition of Monoclinic Hydroxyapatite
    Toshiyuki Ikoma, Atsushi Yamazaki, Satoshi Nakamura, Masaru Akao
    1998 Volume 25 Issue 5 Pages 141-149
    Published: December 30, 1998
    Released on J-STAGE: September 07, 2009
    DOIhttps://doi.org/10.11311/jscta1974.25.141
    JOURNAL FREE ACCESS
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    Monoclinic hydroxyapatite was prepared by a wet method and followed by heating in air at 1473K for 1 hour, and its phase transition was investigated by a high temperature X-ray powder diffractometry and a differential scanning calorimetry. The prepared hydroxyapatite was 98% monoclinic. The Rietveld refinement results revealed that the low temperature phase had monoclinic symmetry, space group P21/b and the high temperature phase had hexagonal symmetry, space group P63/m. In monoclinic hydroxyapatite, two different sizes of oxygen triangles existed. The rotation of phosphate tetrahedra at about 6° and the change of the hydroxyl order to disorder arrangement occurred due to the phase transition. The phase transition took place reversibly at 480.5(1)K in heating process and 477.5(1)K in cooling process. The enthalpy value was found to be 130(1) J mol-1. Further, the transition was observed to resolve into two steps that were attributed to the rotation of phosphate tetrahedra and the order to disorder arrangement of hydroxyls.
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  • General Purpose Cryostat Applicable to Chopped-Light ac Calorimetry with Highly Stable Thermal Condition
    Kazuya Saito, Yasuhisa Yamamura, Michio Sorai
    1998 Volume 25 Issue 5 Pages 150-153
    Published: December 30, 1998
    Released on J-STAGE: September 07, 2009
    DOIhttps://doi.org/10.11311/jscta1974.25.150
    JOURNAL FREE ACCESS
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    An ac calorimeter was constructed for measurements below room temperature. A cryostat was designed while modifying that for adiabatic calorimetry for highly stable thermal condition. Temperature control comparable to that in adiabatic calorimetry was achieved. Chopped-light was introduced to the cryostat through optical fiber, and lead to the sample through a fused-quartz rod. The cryostat is applicable to general physical measurements keeping its capability for thermal control.
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  • Thermal Study of Reentrant Metal-insulator Transition in DCNQI-Cu System
    Yutaka Nishio
    1998 Volume 25 Issue 5 Pages 154-161
    Published: December 30, 1998
    Released on J-STAGE: September 07, 2009
    DOIhttps://doi.org/10.11311/jscta1974.25.154
    JOURNAL FREE ACCESS
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    We have studied the thermal properties of a peculiar and mysterious reentrant metal-insulator (M-I) transition under delicate pressures on DCNQI-Cu system. The measurements of specific heat and latent heat were carried out by thermal relaxation (0.5 < T < 40K), adiabatic pulse (20 < T < 100K) and Differential Thermal Analysis (DTA) methods in the vicinity of the M-I transition controlling the effective pressure. The effective pressure dependence of Sommerfeld constant γ in the metallic phase, temperature dependence of entropy associated with the antiferro-magnetic (AF) ordering of Cu2+ in the insulator phase and latent heat absorbed or released by crossing the M-I transition give the key information on the reentrant M-I transition. From the experimental results, we estimated the free energy in both phases and confirmed that the competition between the freedom of Cu2+ spin system and the free electron near the Fermi energy (γT term) drives the anomalous reentrant metal-insulator transitions.
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