Anomalous low-temperature saturation effects and negative thermal expansion in the c-axis of highly oriented pyrolytic graphite at the magic angle. (20th January 2020)

• Record Type: Journal Article
• Authors: Taallah, Ayoub; Shuai, Gao; Odunmbaku, Omololu; Corrias, Anna; Boi, Filippo S
• Is Part Of: Materials research express. Volume 7:Number 1(2020)
• Publication Date: 2020-01-20
• Subjects: HOPG -- superconductive ordering -- thermal expansion; Materials science -- Research -- Periodicals; Materials science -- Periodicals; 620.11
• DOI: 10.1088/2053-1591/ab6890
• Languages: English
• ISSNs: 2053-1591

Abstract

Abstract: We report a novel T-XRD and Rietveld-refinement investigation of pyrolytic-graphite samples with high degree of graphene-layer-orientation and misfit-rotational-angle of ∼0.8° in the T-range from 12 K to 298 K. An anomalous variation of the graphitic c -axis which involves firstly negative-thermal-expansion (from 12 K to ∼50 K), a saturation-effect (from 50 K to ∼160 K) and then a positive expansion (from ∼180 K to 298 K) is evidenced. The reported trend is significantly different with respect to that expected by considering the standard-thermal-expansion α -parameter where no saturation-effect is present. SQUID-magnetometry revealed further presence of superconducting-like hysteresis which resemble those observed by Scheike et al.