Room temperature charge density wave in a tetragonal polymorph of Gd2Os3Si5 and study of its origin in the RE2T3X5 (RE = Rare earth, T = transition metal, X = Si, Ge) series
arxiv(2024)
Abstract
Charge density wave (CDW) systems are proposed to exhibit application
potential for electronic and optoelectronic devices. Therefore, identifying new
materials that exhibit a CDW state at room temperature is crucial for the
development of CDW-based devices. Here, we present a non-layered tetragonal
polymorph of Gd2Os3Si5, which exhibits a CDW state at room temperature.
Gd2Os3Si5 crystallizes in the U2Mn3Si5-type tetragonal crystal structure with
the space group P4/mnc. Single-crystal x-ray diffraction (SXRD) analysis shows
that Gd2Os3Si5 possesses an incommensurately modulated structure with
modulation wave vector q = (0.53, 0, 0), while the modulation reduces the
symmetry to orthorhombic Cccm(σ00)0s0. This differs in contrast to
isostructural Sm2Ru3Ge5, where the modulated phase has been reported to possess
the superspace symmetry Pm(α 0 γ)0. However, reinvestigation of
Sm2Ru3Ge5 suggests that its modulated crystal structure can alternatively be
described by Cccm(σ00)0s0, with modulations similar to Gd2Os3Si5. The
magnetic susceptibility, ḩi̧(T), exhibits a maximum at low temperatures that
indicates an antiferromagnetic transition at TN = 5.5 K. The ḩi̧(T)
furthermore shows an anomaly at around 345 K, suggesting a CDW transition at
TCDW = 345 K, that corroborates the result from high-temperature SXRD
measurements. Interestingly, R2T3X5 compounds are known to crystallize either
in the tetragonal Sc2Fe3Si5 type structure or in the orthorhombic U2Co3Si5
structure type. Not all of the compounds in the R2T3X5 series undergo CDW phase
transitions. We find that R2T3X5 compounds will exhibit a CDW transition, if
the condition : 0.526 < c/sqrt(ab) < 0.543 is satisfied. We suggest the wave
vector-dependent electron-phonon coupling to be the dominant mechanism of CDW
formation in the tetragonal polymorph of Gd2Os3Si5.
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