Pressure induced strain transition in NiF/sub 2/

Conference · Sat Jan 01 04:00:00 EST 1977

OSTI ID:7289871

Jorgensen, J. D.; Worlton, T. G.; Jamieson, J. C.

Time-of-flight neutron powder diffraction measurements are reported which give the first direct evidence that NiF/sub 2/ undergoes a pressure induced, continuous strain transition from a tetragonal P4/sub 2//mnm (rutile) to an orthorhombic Pnnm structure at 1.83 +- 0.1 GPa. Lattice, structural and thermal parameters have been determined at pressures to 3.24 GPa. Even though the orthorhombic strain is sufficiently small that doublets are not resolved, the use of profile refinement of the diffraction spectra allows us to accurately determine the lattice parameters near the transition and to show that (b - a)/sup 2/ versus pressure is a straight line with slope 2.27 x 10/sup -3/A/sup 2//GPa going to zero at the transition pressure. The measured atomic positions and anisotropic thermal displacements show that motion of the F atoms is responsible for the transition. All of our findings are consistent with a second order transition involving the softening of a transverse acoustic phonon mode propagating along <110> and polarized along <1 anti 10>.

• Research Organization: Argonne National Lab., IL (USA)
• DOE Contract Number: W-31109-ENG-38
• OSTI ID: 7289871
• Report Number(s): CONF-770706-27
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602* -- Other Materials-- Structure &amp; Phase Studies
COHERENT SCATTERING
DIFFRACTION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
LATTICE PARAMETERS
NEUTRON DIFFRACTION
NICKEL COMPOUNDS
NICKEL FLUORIDES
PHASE TRANSFORMATIONS
SCATTERING
STRAINS
TRANSITION ELEMENT COMPOUNDS
VERY HIGH PRESSURE