Elastic anomalies in vanadium chromium sesquioxides

Thesis/Dissertation · Wed Jan 01 04:00:00 EST 1986

OSTI ID:6954761

Yang, H

Transit times of 30 MHz ultrasonic waves were measured in (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/ single crystals with nominal values of x - 0.015, 0.03, and 0.06. Hydrostatic pressures up to about 4 kbar and temperatures between 200 and 650 K were used. The results are used to determine the pressure and temperature dependences of the elastic constants, C/sub ..mu..nu/. Two of the elastic constants, C/sub 11/ and C/sub 12/, have unusual negative pressure dependences resulting in the lambda/sub 4/ elastic eigenvalue decreasing strongly with increasing pressure. This indicates that pressure tends to make the lattice unstable toward a stretching deformation which alters the c/a ratio without changing the crystal symmetry and is consistent with the structural change known to occur at the pressure-induced, paramagnetic insulator-to-metal transition. For (V/sub 0.97/Cr/sub 0.03/)/sub 2/O/sub 3/, the Grueneisen anharmonicity parameter deduced from the elastic data does not agree with that determined from thermal data in contrast to the excellent agreement between the two quantities for pure V/sub 2/O/sub 3/. In all the (V/sub 1-x/Cr/sub x/)/sub 2/O/sub 3/ crystals the C/sub 44/ shear elastic constant softens drastically with decreasing temperature. This, along with other elastic behavior, indicates a smooth change from rhombohedral to almost hexagonal elastic symmetry before a nearly second-order transition to the low-temperature monoclinic phase.

• Research Organization: Purdue Univ., Lafayette, IN (USA)
• OSTI ID: 6954761
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360202 -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360203* -- Ceramics
Cermets
& Refractories-- Mechanical Properties
CHALCOGENIDES
CHROMIUM COMPOUNDS
CHROMIUM OXIDES
CRYSTALS
ELASTICITY
FREQUENCY RANGE
GRUENEISEN CONSTANT
HIGH TEMPERATURE
MECHANICAL PROPERTIES
MEDIUM TEMPERATURE
MHZ RANGE
MHZ RANGE 01-100
MONOCRYSTALS
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
PRESSURE DEPENDENCE
SOUND WAVES
TEMPERATURE DEPENDENCE
TENSILE PROPERTIES
TRANSITION ELEMENT COMPOUNDS
ULTRASONIC WAVES
VANADIUM COMPOUNDS
VANADIUM OXIDES
WAVE PROPAGATION