Low-Temperature Heat Capacity Anomalies in Ordered and Disordered Phases of Normal and Deuterated Thiophene

Y Miyazaki; M Nakano; A I Krivchikov; O A Koroyuk; J F Gebbia; C Cazorla; J Ll Tamarit

doi:10.1021/acs.jpclett.1c00289

Low-Temperature Heat Capacity Anomalies in Ordered and Disordered Phases of Normal and Deuterated Thiophene

J Phys Chem Lett. 2021 Mar 4;12(8):2112-2117. doi: 10.1021/acs.jpclett.1c00289. Epub 2021 Feb 24.

Authors

Y Miyazaki¹, M Nakano¹, A I Krivchikov², O A Koroyuk², J F Gebbia³, C Cazorla⁴, J Ll Tamarit³

Affiliations

¹ Research Center for Thermal and Entropic Science, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka 560-0043, Osaka, Japan.
² B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences Ukraine, 47 Science Avenue, Kharkov 61103, Ukraine.
³ Grup de Caracterizació de Materials, Departament de Física, EEBE and Barcelona Research Center in Multiscale Science and Engineering, Universitat Politècnica de Catalunya, Eduard Maristany, 10-14, Barcelona 08019, Catalonia, Spain.
⁴ Departament de Física, Universitat Politècnica de Catalunya, Campus Nord B4-B5, Barcelona E-08034, Catalonia, Spain.

Abstract

We measured the specific heat C_p of normal (C₄H₄S) and deuterated (C₄D₄S) thiophene in the temperature interval of 1 ≤ T, K ≤ 25. C₄H₄S exhibits a metastable phase II₂ and a stable phase V, both with frozen orientational disorder (OD), whereas C₄D₄S exhibits a metastable phase II₂, which is analogous to the OD phase II₂ of C₄H₄S and a fully ordered stable phase V. Our measurements demonstrate the existence of a large bump in the heat capacity of both stable and metastable C₄D₄S and C₄H₄S phases at temperatures of ∼10 K, which significantly departs from the expected Debye temperature behavior of C_p ≈ T³. This case study demonstrates that the identified low-temperature C_p anomaly, typically referred to as a "Boson-peak" in the context of glassy crystals, is not exclusive of disordered materials.