Electrical conduction in yellow lead oxide has been studied between 500° and 800°C and ionic and electronic contributions separated by means of transport and EMF techniques. The electronic conductivity depends on oxygen partial pressure and on doping. Its dependence on the oxygen pressure is markedly different for samples doped with bismuth or with potassium. It increases with pressure in K‐doped samples; approximately as P 1/n with n between 4 and 6. In Bi‐doped samples a decrease is found wih n between —4 and —6. Information on ionic conduction stems mainly from transport number determinations with the EMF technique. It was found that the ionic conduction, which is carried by oxygen, is independent of the oxygen pressure and increases on the addition of bismuth. Self‐diffusion measurements of oxygen were carried out using the isotope exchange method. It was found that the exchange at the surface is too slow with oxygen gas, but a diffusion‐controlled exchange rate could be obtained with a carbon dioxide gas. The results correspond well with those given by Thompson and Strong; the self-diffusion coefficient at 787°K amounts to about 10−10 cm2/sec. Doping with bismuth increases this value, whereas an influence of potassium dope is not so evident. No influence of the oxygen pressure could be found. Although doping with bismuth causes similar changes in the ionic conductivity and in the self‐diffusion of oxygen, a quantitative comparison suggests that transport of oxygen in neutral form also makes a contribution to the diffusion.
Coloured ferroelectric liquid-crystalline side chain copolymers containing 5 per cent and 15 per cent of an azo dye were synthesized and characterized by DSC, GPC and optical microscopy. Order parameters, S, of the azo compound exceeding 0.8 were measured in the frozen smectic phase for the 5 per cent copolymer. The copolymers exhibit fast electrooptic switching in the range of a few hundred microseconds to milliseconds in the S$ phase. Both linear (i.e. electroclinic-like) and ferroelectric switching have been observed. Tilt angles of -19" and spontaneous polarization of -300nCcm-' have been recorded in the S$ phase. IntroductionResearch in ferroelectric liquid crystals has been intense over the past few years. One important advantage of ferroelectric displays compared with the well-known and widely used twisted nematic or supertwist nematic displays is the fast electrooptic switching which is in the range of microseconds. Recently the first examples of switchable ferroelectric liquid crystal side chain polymers have been reported [ 1-41. In favourable cases [3,4] we found response times in the range of some hundred microseconds. Because of the relatively poor anti-shock characteristics of surface stabilized low molar mass ferroelectric display devices fast switching ferroelectric liquid crystal polymers, which form robust films, may find future applications using various birefringent or absorption based electrooptic effects.Coloured liquid crystal displays applying the guest host effect of dichroic dyes dissolved in a nematic liquid crystal were developed some years ago [S]. Recently the guest host effect of dichroic dyes in a ferroelectric liquid crystal [6] and, for the first time, in ferroelectric liquid crystal polymers has been investigated [7]. One drawback to this effect is the poor solubility of dyes in both low molar mass and polymeric liquid crystal materials. By copolymerization of dye monomers a higher percentage of dye content has been achieved in nematic polymers [S]. Ferroelectric liquid crystal dye copolymers, hitherto unknown, might be expected to have both fast switching properties, associated with the ferroelectric phase, and high colour contrast in thin films, because of the higher order parameter and solubility of suitable dyes in the smectic S z layers.
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