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.
Phase Diagrams for Ferroelectric-Antiferroelectric Mixed System
The model for mixed ferroelectric-antiferroelectric system is proposed. Each crystalline lattice site is occupied by a cluster of “spin” particles, total momentum of a cluster can be oriented only in one of the two perpendicular directions: along z or along x axis, n is the concentration for the z-type component, 1 − n is the same for the x-type one. We account for both long and short ranged interactions between particles and use the cluster approximation to calculate the partition function of the investigated system. The phase diagrams, the paraelectric-ferroelectric and paraelectric-antiferroelectric phase transitions are discussed together with the possibility of the “spin-glass” phase existence. The model being proposed can be used in the problems of thermodynamics for a large class of Kn(NH 4 ) 1−nH2PO 4 -type mixed compounds.
Chromatographic analysis of elastomer antidegradants and accelerators
Summary The use of various chromatographic methods in the analysis of all classes of elastomer antidegradants and accelerators is reviewed. The review of extraction methods is also included.