Specific-heat anomaly caused by ferroelectric nanoregions in Pb(Mg(1/3)Nb(2/3))O3 and Pb(Mg(1/3)Ta(2/3))O3 relaxors

The specific heat of typical relaxors, Pb(Mg(1/3)Nb(2/3))O3 (PMN) and Pb(Mg(1/3)Ta(2/3))O3 (PMT), was measured by adiabatic and relaxation methods between 2 and 420 K. A broad anomaly was found in the specific heat curve over the wide temperature range between 150 and 500 K for PMN, and between 50 and 400 K for PMT, which provides evidence for the formation of ferroelectric nanoregions (FNR) in the paraelectric matrix. The entropy of the anomaly was estimated as 3.3 J K(-1) mol(-1) and 2.9 J K(-1) mol(-1) for PMN and PMT, respectively, which implies an order-disorder-type mechanism for the formation of FNR.     

Effect of inelastic scattering processes on (p,t) reactions exciting the first 2+ states in Te,Sn and Cd isotopes

Differential cross sections of (p, t) reactions exciting the 2⁺₁ states in Te (A = 128 ? 120), Sn (116 and 114) and Cd (114 and 112) have been measured at E_p = 52 MeV. The observed differences of the angular distributions are interpreted by taking into account the two-step processes through inelastic scattering channels.     

Heat capacity anomalies due to successive phase transitions in 1,1′-biphenyl

Precision heat capacity measurements on 1,1′-biphenyl revealed two broad anomalies at 11.0 K and 40.4 K. The excess enthalpies and entropies are 0.28 ± 0.02 J mol^?1 and 0.026 ± 0.002 J K^?1mol^?1 for the anomaly extending from 7.5 to 14.0 K, and 5.02 ± 0.08 J mol^?1 and 0.129 ± 0.003 J K^?1mol^?1 for the anomaly extending from 30.0 to 47.0 K, respectively. A possible molecular mechanism is suggested.     

Orientation of the remaining amorphous chains during crystallization: Isotactic polystyrene

The orientation of statistical chain segments in the amorphous regions of a semicrystalline polymer can be characterized quantitatively by x-ray diffraction. A calculated background (which is orientation independent) must be subtracted, which requires that the intensity profile of the amorphous halo be measured on an absolute scale. Application is illustrated to samples of isotactic polystyrene which were isothermally crystallized at fixed elongation. These samples differ from those of the previous study due to the unintentional introduction of a small amount of crystallinity (0.25% to 1%) which serves as tie points in the drawing operation, giving a stronger amorphous orientation. Preferred orientation of the amorphous chain segments is rapidly depleted during the first few percent of crystallization. The crystallite orientation distribution is quite sharp, and broadens only slowly with crystallization. These results imply that, for the crystallization conditions employed, the crystallite orientation must be determined by nuclei which are formed at the earliest stages of the crystallization process.     

Fiber-Optic Ammonia Sensors Utilizing Rectangular-Cladding Eccentric-Core Fiber

A new fiber-optic ammonia sensor utilizing rectangular-cladding eccentric-core fiber and a sensitive film containing an indicator dye is demonstrated. The sensitive film is a SiO₂-GeO₂ gel film including an indicator dye of bromocresol purple or bromocresol green, which is dip-coated by a sol-gel technique. The attenuation of this sensor changes depending on the concentration of ammonia at the wavelength range of 500–700 nm. This sensor can detect several ppm of gaseous ammonia. Various factors determining the sensitivity to detect the ammonia gas and time response of the sensor are also studied.     

Anionic polymerization of styrene in the presence of pyridine

An interesting effect of pyridine on the anionic polymerization of styrene in THF is described. Pyridine forms a complex with living polystyrene and greatly slows the polymerization rate without changing the degree of polymerization. From kinetic and spectroscopic studies, it was clear that there exist two active species in this system and the complex between living polystyrene and pyridine was of the 1:1 type, which itself had a weak ability to grow. The formation constant of the complex K was found to be about 4 × 10⁵ l./mole. The effect of substituted pyridine was also studied and the nature of the complex was discussed.     

New high-pressure polymorphs in sodium halides

Static compression experiments to 50 GPa, employing X-ray diffraction through a diamond cell, were made on NaF, NaBr and NaI. NaF was found to transform from its initial B1 (NaCl-type) to the B2 (CsCl-type) structure at 27 ± 1GPa on the ruby fluorescence scale with a volume change at the transition of ?8.9%. New high-pressure polymorphs showing birefringence under microscope were found both for NaBr and NaI at 29 ± 1 GPa and 26 ± 1 GPa, respectively. X-ray diffraction patterns of these high-pressure polymorphs could not be indexed as the B2 structure. The GeS-type structure (the distorted NaCl structure) was tentatively assigned to the high-pressure polymorph of NaI.