Effects of pressure on the dielectric properties and phase transitions of the 2-D antiferroelectric squaric acid: (H/sub 2/C/sub 4/O/sub 4/ and D/sub 2/C/sub 4/O/sub 4/)
The pressure dependences of the dielectric properties and phase transitions of squaric acid, H/sub 2/C/sub 4/O/sub 4/, and its deuterated analog, D/sub 2/C/sub 4/O/sub 4/, were investigated. The transition temperatures at 1 bar are 375.5 +- 1.0 K and 527.5 +- 2.0 K, respectively, and decrease with pressure at initial rates of 105.6 +- 2.0 K/GPa and 102.5 +- 2.0K/GPa. It is argued that the large hydrogen isotope effect on T/sub c/ can be accounted for on the basis of the elongation of the O--HxxxO bond resulting from deuteration. This elongation causes a modification of the double-well potential along this bond. It is not necessary to invoke proton tunneling. The lack of an appreciable isotope effect on dT/sub c//dP supports the absence of tunneling. An interesting aspect of the results is the appearance of a dome-shaped feature in the real part of the dielectric constant just above T/sub c/ in both crystals. This feature, which is reminiscent of the behavior of the magnetic susceptibility of antiferromagnets above the Neel temperature, is discussed. The results on D/sub 2/C/sub 4/O/sub 4/ suggest the possible existence of a pressure-induced phase transition at approx.0.8 GPa. The dielectric loss of this crystal is large both below and above T/sub c/. This is attributed to the high conductivity of D/sub 2/C/sub 4/O/sub 4/ on approaching the melting (or dissociation) temperature. The activation energies for conduction and their pressure dependences both above and below T/sub c/ are determined and discussed.
- Research Organization:
- Sandia Laboratories, Albuquerque, New Mexico 87185
- OSTI ID:
- 5939588
- Journal Information:
- J. Chem. Phys.; (United States), Journal Name: J. Chem. Phys.; (United States) Vol. 71:3; ISSN JCPSA
- Country of Publication:
- United States
- Language:
- English
Similar Records
Study of the structure of PyHReO{sub 4} under high pressure
Molecular and crystal structure of squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione) at 121 /sup 0/C: A neutron diffraction study
Related Subjects
360603* -- Materials-- Properties
ANTIFERROELECTRIC MATERIALS
CHEMICAL REACTIONS
DEUTERATION
DEUTERIUM
DIELECTRIC MATERIALS
DIELECTRIC PROPERTIES
ELECTRICAL PROPERTIES
HYDROGEN ISOTOPES
ISOTOPE EFFECTS
ISOTOPES
LIGHT NUCLEI
MATERIALS
NUCLEI
ODD-ODD NUCLEI
ORGANIC ACIDS
ORGANIC COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
PRESSURE DEPENDENCE
STABLE ISOTOPES