title: Low-Temperature Anharmonicity in Cesium Chloride (CsCl).
abstract: Anharmonic lattice vibrations govern heat transfer in materials, and anharmonicity is commonly assumed to be dominant at high temperature. The textbook cubic ionic defect-free crystal CsCl is shown to have an unexplained low thermal conductivity at room temperature (ca. 1 W/(m K)), which increases to around 13  W/(m K) at 25 K. Through high-resolution X-ray diffraction it is unexpectedly shown that the Cs atomic displacement parameter becomes anharmonic at 20 K.
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000, Aarhus, Denmark.
authors.forename: Mattia
authors.initials: M
authors.lastname: Sist
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000, Aarhus, Denmark.
authors.forename: Karl Frederik Faerch
authors.initials: KF
authors.lastname: Fischer
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000, Aarhus, Denmark.|Faculty of Pure and Applied Sciences, TIMS and CiRfSE, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, 305-8571, Japan.
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Kasai
authors.affiliation: Center for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, Langelandsgade 140, 8000, Aarhus, Denmark.
authors.forename: Bo Brummerstedt
authors.initials: BB
authors.lastname: Iversen
keywords: NXMEM; anharmonicity; cesium chloride; low thermal conductivity; thermoelectric