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Abstract:
We used low-temperature synchrotron x-ray diffraction to investigate the structural phase transitions of Fe1+y Te in the vicinity of a tricitical point in the phase diagram. A detailed analysis of the powder diffraction patterns and temperature dependence of the peak widths in Fe1+y Te showed that two-step structural and magnetic phase transitions occur within the compositional range 0.11 <= y <= 0.13. The phase transitions are sluggish, indicating a strong competition between the orthorhombic and the monoclinic phases. We combine high-resolution diffraction experiments with specific heat, resistivity, and magnetization measurements and present a revised temperature-composition phase diagram for Fe1+y Te.