Incommensurate lattice-instability in K/sub 2/SeO/sub 4/

Conference · Thu Jan 01 04:00:00 EST 1976

OSTI ID:7258657

Iizumi, M; Axe, J D; Shirane, G; Shimaoka, K

Successive phase transformations in K/sub 2/SeO/sub 4/ at T/sub i/ = 130K and T/sub c/ = 93K have been studied by the triple-axis neutron scattering technique. Above T/sub i/ a SIGMA/sup 2/ optic phonon branch along (xi,0,0) shows striking softening and ..omega..(vector q) for vector q approximately (1/3,0,0) tends to zero at T/sub i/. This softening results from a temperature dependent decrease of the interlayer forces with range a/2 and a (a is one unit cell length along the a axis) in the presence of strong and persisting forces with a range 3a/2. The critical scattering above T/sub i/ has a maximum at an incommensurate position: vector q/sub delta/ = (1-delta) vector a*/3 with delta approximately 0.08 and peaks at E = 0 near T/sub i/. At T/sub i/ superlattice reflections appear at incommensurate positions, vector q/sub delta/. The deviation delta decreases with decreasing temperature with an apparently discontinuous jump to delta = 0 at T/sub c/. Below this temperature the crystal remains commensurate and is ferroelectric. The incommensurate transition, the simultaneous lock-in of the commensurate phase and the ferroelectricity are discussed using a Landau type expansion of the free energy.

• Research Organization: Brookhaven National Lab., Upton, N.Y. (USA)
• Sponsoring Organization: US Energy Research and Development Administration (ERDA)
• DOE Contract Number: E(30-1)-16
• OSTI ID: 7258657
• Report Number(s): BNL-21471; CONF-760601-5
• Country of Publication: United States
• Language: English

Related Subjects

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73 NUCLEAR PHYSICS AND RADIATION PHYSICS
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALI METAL COMPOUNDS
CHALCOGENIDES
COHERENT SCATTERING
DIFFRACTION
INSTABILITY
LATTICE PARAMETERS
NEUTRON DIFFRACTION
OXIDES
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
PHONONS
POTASSIUM COMPOUNDS
QUASI PARTICLES
REFLECTION
SCATTERING
SELENIUM COMPOUNDS
SUPERLATTICES