COEXISTENCE OF PARAELECTRIC/PROTON-GLASS AND FERROELECTRIC (ANTIFERROELECTRIC) ORDERS IN Rb_{1-x}(NH_{4})_{x}H_{2}AsO_{4} CRYSTALS
This paper reviews the results of dielectric studies of the proton glass state in a mixed crystal Rubidium Ammonium Dihydrogen Arsenate (RADA) The coexistence of paraelectric/proton glass and ferroelectric or antiferroelectric orders, confirmed by other studies, has been discussed in detail. The phase diagram of RADA is asymmetric. The proton glass state exists for ammonium concentration in the range of 0.1 < x < 0.5 . The phase diagram of deuterated DRADA is presented. The proton glass state region in DRADA, 0.2 < x < 0.35 is narrower than that for non-deuterated RADA. The effects of hydrostatic pressure on the dielectric properties in the proton glass state are presented. The glass temperature Tg decreases with pressure and is expected to vanish at 5 kbar. Low temperature behaviour is still an open question, since there is no experimental evidence of Tg(p) dependence below 4K for proton glass systems.
Dielectric Dispersion in Rb1-x[N(H1-yDy)4]x(H1-yDy)2PO4 Mixed Crystal System
Temperature and frequency dependent dielectric responses of Rb 1- x [N(H 1- y D y ) 4 ] x (H 1- y D y ) 2 PO 4 (0.25≤ x ≤0.75, 0≤ y ≤1.0) have been measured from 4.2 K to 300 K and between 1 kHz and 1 GHz. The glass-like dielectric dispersion was found in the low temperature region. The relaxation time τ has been confirmed to follow the Vogel-Fulcher law, τ=τ 0 exp [ E /( T - T 0 )], with a temperature independent Gaussian distribution of energy parameter E . Pronounced effect of deuteration was found in the dynamical dielectric properties. On the contrary, there is no obvious x dependence in the dynamical properties. Little difference was observed in the dielectric dispersions along the a - and c -axes. These results indicate that proton motion in the O-H···O bond has decisive role in the glass-like behavior.
A Rapid Method for the Extraction of Radioiodide from Urine
THE extraction of radioiodide from urine is important in radioiodide therapy, since without it the large quantities of highly radioactive urine which accumulate must be stored until the activity decays sufficiently to allow disposal.