l'lic full-faccd crystals of triglycinc sulphate (TGS) and deuterated hornologs substituted by I4-a1aniiio (LATGS arid LADTGS, resp.) wcrc grown from growth solutions with various concentratloris of the sribstituerit. The distribution of L, alanirie (L,al) in various growth pyramids of crystals was measured by the electrical switching method. Tho stability of domain structure of doped crystals was studied by the liquid crystal method.

h drscriptioii of the various orientations of microstructure and large single crystals of triglycine sulphate (TGS) is reviewed. A difference of the orielitation of TGS in polydornain statc anti in two possible singledomain states is discussed. The conclusions arc applied t o TGS crystals doped with L, alariirie or U, alanine.

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Dielectric spectroscopy data in the frequency range 100 Hz -10 MHz are presented for two kinds of Rb&ZnC14 crystals, purified and standard quality, with special attention to the lock-in ferroelectric phase (C phase). It is shown that unlike standard-quality samples, the permittivity c tail extends deep into the C phase of purified crystals and is an almost unambiguous function of temperature. The c(T) dependence and its dispersion properties show that the temperature region below the incommensurate (IC) phase can be divided into four sections. On cooling, the first-order transformation takes place within the interval AT, in which de, /dT (0 and the relaxation frequency drops by almost two orders of magnitude.Here the IC and C phases coexist, the discommensurations change into domain walls (DW's) while their density considerably decreases. In the neighboring interval AT& permittivity still continues to grow;Cole-Cole plots show a nearly Debye behavior, with relaxation frequency f, decreasing fast from 3.6 MHz to about 800 kHz when the low-frequency e reaches its peak value at the temperature T . Here as well as in the subsequent intervals permittivity is given by DW contributions. The data in b Tl are well explained by assuming that the wall interaction is repulsive and given by the same law as in the IC phase.At T the wall motion begins to be predominantly determined by pinning to lattice defects. Below T in the intervals hT& and ET3, each several decakelvin wide, dc, /dT )0. In AT& a Debye-like relaxation dominates. The mean relaxation time fulfills the Arrhenius law and the wall-motion mechanism is believed to be thermally activated. Below, in the interval ET3, it is replaced by another mechanism characterized by low-frequency relaxation tails extending below the measuring frequency range.