Phase Transitions in the Brominated Ferroelectric Tris‐Sarcosine Calcium Chloride
paraelectrics SrTiO 3 and KTaO 3 . [ 9 ] However, the ultra-weak nature of the dipole moment in TSCC referred to below may reduce the effects of such long-range dipole interactions to a narrow temperature region around the critical point. This would mean that more conventional classical or quantum critical behaviour would be expected over a wider range of temperatures and tuning parameters. TSCC is hydrogen bonded and was characterized in the past as order-disorder albeit with no direct supporting evidence. [ 16,17 ] Since the time of these studies TSCC has come to be a prototypical displacive ferroelectrics, [ 18 ] as demonstrated by the existence of an under-damped soft mode. This mode can be followed into the GHz frequency regime [ 19 ] from highT values of ca 630 GHz = 21 cm −1 . Deuteration [ 20 ] produces little change in T C , implying that the transition is not controlled by the N-Cl-hydrogen bonds, a result compatible with the soft-mode mechanism operating in TSCC. [ 2 ]
Ferroelectric Relaxor Quantum Crystals
A discussion is given of ferroelectrics (FEs) that have their Curie temperatures Tc very near absolute zero. These have differences in their dynamics in comparison with higher-temperature systems, since domain wall motion occurs via quantum mechanical tunneling and not by thermally activated diffusion. Emphasis in the present paper is on FEs that have relaxor characteristics. In such systems, the temperature at which the isothermal electric susceptibility e(T,f) peaks is a strong function of frequency, and it decreases with decreasing frequency. This is due to glassy viscosity and is symbolic of non-equilibrium dynamics, usually described by a Vogel-Fulcher equation. It permits an extra dimension with which to examine the transitions. The second half of this paper reviews domain wall instabilities and asks about their presence in QCP ferroelectrics, which has not yet been reported and may be unobservable due to the absence of thermal diffusion of walls near T = 0; in this respect, we note that diffusion does exist in ferroelectric relaxors, even at T = 0, by virtue of their glassy, viscous dynamics.
The Accuracy of Reported Insurance Status in the MEPS
Estimates of the number of insured and uninsured Americans are watched by numerous policymakers and the public, yet studies find respondents do not report their insurance status perfectly. Using four sources of validation data, including surveys of employers and providers, this paper assesses the quality of respondents' reports of private insurance and uninsurance in the Medical Expenditure Panel Survey Household Component (MEPS-HC), a nationally representative household survey. Regression analysis is used to assess the extent to which factors are associated with disagreements in reported insurance status across sources.