title: Colossal positive and negative thermal expansion and thermosalient effect in a pentamorphic organometallic martensite.
abstract: The thermosalient effect is an extremely rare propensity of certain crystalline solids for self-actuation by elastic deformation or by a ballistic event. Here we present direct evidence for the driving force behind this impressive crystal motility. Crystals of a prototypical thermosalient material, (phenylazophenyl)palladium hexafluoroacetylacetonate, can switch between five crystal structures (α-ε) that are related by four phase transitions including one thermosalient transition (α↔γ). The mechanical effect is driven by a uniaxial negative expansion that is compensated by unusually large positive axial expansion (260 × 10(-6)  K(-1)) with volumetric expansion coefficients (≈250 × 10(-6)  K(-1)) that are among the highest values reported in molecular solids thus far. The habit plane advances at ~10(4) times the rate observed with non-thermosalient transitions. This rapid expansion of the crystal following the phase switching is the driving force for occurrence of the thermosalient effect.
authors.affiliation: Division of Sciences and Mathematics, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: Manas K
authors.initials: MK
authors.lastname: Panda
authors.affiliation: Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Tomče
authors.initials: T
authors.lastname: Runčevski
authors.affiliation: Division of Sciences and Mathematics, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: Subash Chandra
authors.initials: SC
authors.lastname: Sahoo
authors.affiliation: International Center for Materials Nanoarchitectonics (WPI-MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Alexei A
authors.initials: AA
authors.lastname: Belik
authors.affiliation: Division of Sciences and Mathematics, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: Naba K
authors.initials: NK
authors.lastname: Nath
authors.affiliation: Max Planck Institute for Solid State Research, Heisenbergstrasse 1, D-70569 Stuttgart, Germany.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Dinnebier
authors.affiliation: Division of Sciences and Mathematics, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
authors.forename: Panče
authors.initials: P
authors.lastname: Naumov