Accession Number:

ADA172349

Title:

On the Phase Transition of N-Isopropylcarbazole.

Descriptive Note:

Technical rept.,

Corporate Author:

COLORADO STATE UNIV FORT COLLINS DEPT OF CHEMISTRY

Personal Author(s):

• Nowak,R.
• Bernstein,E. R.

Report Date:

1986-05-01

Pagination or Media Count:

42.0

Abstract:

The elastic properties of N-isopropylcarbazole NIPC, a pyroelectric molecular crystal, are investigated by Brillouin scattering. The full elastic constant tensor is determined at 295 K and the temperature dependence of the elastic constants are given. The major experimental finding reported is the anomaly of the LA a-axis mode governed by the c sub 11 elastic constant. This mode exhibits a pronounced downward bending on both sides of the nonferroic, first order phase transition at ca. 137 K. Symmetry allowed linear-quadratic and biquadratic couplings between the Brillouin zone boundary one-dimensional order parameter and the zone center strain introduced into the Landau free-energy do not account for the observed anomaly. The transition is characterized in terms of a strong dispersion of the c sub 11 elastic constant and a large dynamical critical behavior. By combining the c sub 11 elastic constant data and the Brillouin scattering LA a-axis mode halfwidth data through a Landau-Khalatnikov process, a relaxation time is extracted satisfying mean-field dependence characteristic of critical slowing down of the order parameter.

Descriptors:

• *PHASE TRANSFORMATIONS
• *CRYSTALS
• *PYRROLES
• *BENZYL RADICALS
• *PROPYL RADICALS
• LIGHT SCATTERING
• TEMPERATURE
• DYNAMICS
• MOLECULES
• PARAMETERS
• ELASTIC PROPERTIES
• STRAIN(MECHANICS)
• BENDING
• PIEZOELECTRIC CRYSTALS
• CONSTANTS
• TRANSITIONS
• RELAXATION TIME
• TENSORS
• PYROELECTRICITY
• BRILLOUIN ZONES

Subject Categories:

• Physical Chemistry
• Electrical and Electronic Equipment

Distribution Statement:

APPROVED FOR PUBLIC RELEASE