THERMODYNAMICS OF THE ANION ORDERING TRANSITIONS IN (TMTSF)2REO4 AND (TMTSF)2BF4

Citation
M. Chung et al., THERMODYNAMICS OF THE ANION ORDERING TRANSITIONS IN (TMTSF)2REO4 AND (TMTSF)2BF4, Physical review. B, Condensed matter, 48(13), 1993, pp. 9256-9263
Citations number
37
Categorie Soggetti
Physics, Condensed Matter
ISSN journal
01631829
Volume
48
Issue
13
Year of publication
1993
Pages
9256 - 9263
Database
ISI
SICI code
0163-1829(1993)48:13<9256:TOTAOT>2.0.ZU;2-T
Abstract
We have studied the anion ordering transitions in the Bechgaard salts, (TMTSF)2ReO4 and (TMTSF)2BF4 using ac calorimetry, differential scann ing calorimetry, and the vibrating-reed technique. An analysis of the sensitivity of ac calorimetry to (distributed) molar latent heat l(T) is presented. For the ReO4 salt, the transition is weakly first order, exhibiting no sluggishness or hysteresis. The effective specific heat measured using ac calorimetry, i.e., c(p) + dl/dT, exhibits a lambda- like anomaly, but the entropy of the transition is sample dependent an d generally less than the expected value, R ln(2). In comparison, the transition is sluggish for the tetrafluoroborate salt, so that only a lower limit on the entropy could be determined. The thermal anomalies are compared to the anomalies observed using the vibrating-reed techni que; the latter are affected by changes in the lattice constants as we ll as the Young's moduli at the transitions.