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Structural Phase Transitions in CaC 2
Author(s) -
Knapp Michael,
Ruschewitz Uwe
Publication year - 2001
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/1521-3765(20010216)7:4<874::aid-chem874>3.0.co;2-v
Subject(s) - phase (matter) , physics , quantum mechanics
Pure CaC 2 , free of CaO impurities, was obtained by the reaction of elemental calcium with graphite at 1070 K. By means of laboratory X‐ray and synchrotron powder diffraction experiments, the phase diagram was investigated in the temperature range from 10 K to 823 K; this confirmed the literature data that reported the partial coexistence of up to four modifications. Aside from a cubic high‐temperature modification CaC 2 IV ( Fm $\bar 3$ m, Z =4) and the well‐known tetragonal modification CaC 2 I ( I 4/ mmm, Z =2), a low‐temperature modification CaC 2 II ( C 2/ c, Z =4) that crystallizes in the ThC 2 structure type and a metastable modification CaC 2 III ( C 2/ m, Z =4) that crystallizes in a new structure type were found. It was shown that phase transition temperatures as well as the relative amounts of the various CaC 2 modifications depend upon the size of the crystallites, the thermal treatment, and the purity of the sample, as a comparison with technical CaC 2 confirmed.