Phase change and pyroelectricity in natural hemimorphite |
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Authors: | N F Cano E A Gallegos S Watanabe |
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Institution: | 1. Institute of Physics , University of S?o Paulo , Rua do Mat?o, Travessa R, 187, CEP 05508-900, S?o Paulo, 66318, Brazil nilocano@dfn.if.usp.br nfcano@gmail.com;3. Institute of Physics , University of S?o Paulo , Rua do Mat?o, Travessa R, 187, CEP 05508-900, S?o Paulo, 66318, Brazil |
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Abstract: | The phase change of a natural hemimorphite sample from Minas Gerais (Brazil) was investigated by two X-ray diffraction (XRD) methods and by near-infrared reflectance spectroscopy. Applying successive thermal treatments, the crystal structure undergoes two orientation conversions. The first one occurs at about 550 °C, and it was revealed by the Laue method. Below 500 °C, the water molecules were partially expelled without changing the crystal structure. A fact that supports this statement is the sequential disappearance of the water bands at 1400 and 1900 nm by thermal treatment. The second conversion takes place below 939 °C. Moreover, at 972 °C a phase change to the willemite mineral (α-Zn2SiO4) has been observed. This last conversion was confirmed by the power XRD. In addition, natural hemimorphite displayed a high pyroelectricity, which is related both to the absence of inverse centre and to the presence of molecular water and hydroxyl groups in the crystal structure. |
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Keywords: | phase change near-infrared X-ray diffraction pyroelectricity |
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