title: Structural transition of PETN-I to ferroelastic orthorhombic phase PETN-III at elevated pressures.
abstract: Using powder x-ray diffraction and first-principles calculations, we provide evidence for a structural transition of PETN-I below 6 GPa to an orthorhombic phase of space group P2(1)2(1)2. The transition can be rationalized as shear-stress induced and ferroelastic, which involves a slight static displacement of the molecules that breaks the fourfold symmetry of PETN-I. Previously reported changes in the optical spectra reflect a lifting of the twofold degeneracy of modes in tetragonal PETN-I. The observed transition is expected to induce soft shear compliances along specific directions in PETN crystallites that may relate to the observed dependence of detonation pressure on crystal orientation.
authors.affiliation: High Pressure Science and Engineering Center, Department of Physics, University of Nevada, Las Vegas, Nevada 89154, USA.
authors.forename: O
authors.initials: O
authors.lastname: Tschauner
authors.forename: B
authors.initials: B
authors.lastname: Kiefer
authors.forename: Y
authors.initials: Y
authors.lastname: Lee
authors.forename: M
authors.initials: M
authors.lastname: Pravica
authors.forename: M
authors.initials: M
authors.lastname: Nicol
authors.forename: E
authors.initials: E
authors.lastname: Kim