{"created":"2023-06-19T10:29:16.736667+00:00","id":9051,"links":{},"metadata":{"_buckets":{"deposit":"73d4cf20-3134-4ccd-bc14-206e32d7af2a"},"_deposit":{"created_by":18,"id":"9051","owners":[18],"pid":{"revision_id":0,"type":"depid","value":"9051"},"status":"published"},"_oai":{"id":"oai:muroran-it.repo.nii.ac.jp:00009051","sets":["41:227"]},"author_link":["53652"],"item_81_date_granted_17":{"attribute_name":"学位授与年月日","attribute_value_mlt":[{"subitem_dategranted":"2016-09-28"}]},"item_81_degree_grantor_10":{"attribute_name":"学位授与機関","attribute_value_mlt":[{"subitem_degreegrantor":[{"subitem_degreegrantor_language":"ja","subitem_degreegrantor_name":"室蘭工業大学"},{"subitem_degreegrantor_language":"en","subitem_degreegrantor_name":"Muroran Institute of Technology"}],"subitem_degreegrantor_identifier":[{"subitem_degreegrantor_identifier_name":"10103","subitem_degreegrantor_identifier_scheme":"kakenhi"}]}]},"item_81_degree_name_11":{"attribute_name":"学位名","attribute_value_mlt":[{"subitem_degreename":"博士（工学）","subitem_degreename_language":"ja"}]},"item_81_description_25":{"attribute_name":"フォーマット","attribute_value_mlt":[{"subitem_description":"application/pdf","subitem_description_type":"Other"}]},"item_81_description_7":{"attribute_name":"抄録","attribute_value_mlt":[{"subitem_description":"In some rare earth compounds, valences of rare earth elements take non-integer values, because valence values of rare earth elements fluctuate spatially and temporally. The fluctuated valences depend strongly on the synthesis temperature. In this study, Yb, Eu, Sm based sulfides with valence-fluctuation characters were to study the synthesis and stability and expected to discover new applications.\nYtterbium sulfides were prepared from CS2 sulfurization of Yb2O3 and then heat treatments. Ytterbium sulfides (Yb3S4 and YbS) are expected to be employed as high temperature n-type thermoelectric materials due to their large Seebeck coefficient. \nThe influences of particle size and specific surface area of Yb2O3 powders, sulfurization temperature and time and CS2 gas flow rate on preparation of ytterbium sesquisulfide (Yb2S3) were researched. Small particle size (< 1 μm) and large specific surface area (> 2 m2/g) of Yb2O3 are necessary for fabrication of pure Yb2S3. Single orthorhombic η-Yb2S3 and hexagonal ε-Yb2S3 were synthesized by the sulfurization of fine Yb2O3 powders at 973～1073 K and 1273～1323 K with CS2 gas flow rate of 1.67 mL/s, respectively. Orthorhombic η-Yb2S3 transformed to hexagonal ε-Yb2S3 with increase of temperature. The heat treatments of Yb2S3 were investigated. Upon heat treatment at 1273 K for 3 hr in Ar/CS2 atmosphere, orthorhombic Yb2S3 phase underwent phase transition to hexagonal Yb2S3 phase. Moreover, orthorhombic Yb3S4 was main phase after heat treatment at 1050°C for 8 hr under Ar atmosphere and Yb2S3 disappeared upon prolonged (12 hr) heat treatment. Single Yb3S4 phase could be obtained after treatment at 1273 K for 3 hr, or at 1473 K for 1 hr, under vacuum (～1.2×10-3 Pa). Single-phase YbS with a homogeneity range of YbS1.11-1.15 could be synthesized by treatment at 1773 K for 3 hr. \nSecondly, europium sulfides were synthesized by CS2 sulfurization of Eu2O3. EuS is a ferromagnetic semiconductor with NaCl type crystal structure. As this temperature is in the proximity of the boiling point of hydrogen, EuS is a potential magnetic refrigeration material. \nThe effects of Eu2O3 character and sulfurization conditions on the preparation of europium sulfides were researched. Single-phase Eu3S4 and EuS can be obtained by CS2 gas sulfurization of spherical Eu2O3 with larger specific surface area and small grain size at 773 K for longer than 0.5 hr and 1073 K for 8 hr, respectively. Moreover, EuS can be fabricated from self-prepared needle Eu2O3 at 1023 K for 8 hr. The higher sulfurization temperature and shorter sulfurization time accelerated the formation of high purity EuS. Specific surface area of synthetics lessened with the rising of sulfurization temperature and time. Synthetic pure Eu3S4 were treated under rich-sulfur atmosphere, inert atmosphere and vacuum, respectively. Single EuS phase was obtained at 973 K under rich-sulfur atmosphere or at 1073 K under inert atmosphere. The stability of Eu3S4 during annealing is weaker than all above mentioned conditions and the transformation finished at 873 K under vacuum of 1.2×10-5 Pa. The transformation of Eu3S4 to EuS was attributed to stability of Eu2+ at high temperature. The synthetic EuS powders were sintered under a uniaxial pressure of 50 MPa in vacuum. The large reversible magnetocaloric effect of polycrystalline EuS was observed, which underwent second-order ferromagnetic to paramagnetic transition at 16.8 K. The maximum of magnetic entropy change is as large as 6.32 J/mol/K and the adiabatic temperature change is 9.1 K under a vary magnetic field change of 5 T. The entropy value for polycrystalline EuS was revised by the combination of the magnetization and heat capacity data. The relative cooling power for polycrystalline EuS reached 69.26 and 125.39 J/mol for ΔH = 3 T and 5 T, respectively. \nFinally, non-stoichiometric samarium monosulfide (SmSx, 0.55