CC Values Research Articles

Evaluation of curie constants of ferroelectric crystals from pyroelectric response

Abstract A method is described for determining the Curie constant (Cc) of ferroelectric crystals below the Curie temperature (Tc) from the pyioelectric response. It is shown from Devonshire's phenomenological theory of ferroelectricity that the material parameter (p/ϵ) of the pyroelectric response is given by p/ϵ =PS/Cc , where Ps is the spontaneous polarization. This relationship is tested in detail for Sr0.5Ba0.5Nb2O6 crystals. The value of Cc obtained from the Curie-Weiss law, ϵ = CC /(T - Tc ), which is valid above Tc , is compared to the value of Cc obtained below Tc for SBN and other ferroelectric crystals and reasonable agreement is observed.

Relationship between polymer concentration and molecular weight in the viscosity behavior of concentrated solution

Solution viscosities of acrylonitrile copolymer samples with different molecular weights were determinated at different polymer concentrations with aMaron-Krieger-Sisko viscometer. Double logarithmic plots between zero-shear viscosity and polymer concentration thus obtained were fit by two straight lines with different slopes. A critical concentration,Cc, was then defined as the concentration at which these straight lines meet with each other. The value ofCc evaluated with each sample was found to depend on molecular weight of the sample,M, in a following fashion: $$C_e \cdot M^a = const.$$ . The exponent,a, was different for different molecular weight range and amounted to 0.5 and 1.0 within enough of a low and a high molecular weight range, respectively. This variation of “a” was different from that observed byCornet and was discussed in terms of the excluded volume effect in polymer coils.

Proton chemical shifts in saturated hydrocarbons

The proton chemical shifts of a number of relatively unstrained hydrocarbons have been analysed in terms of the local diamagnetic shielding and long-range shielding by carbon-carbon single bonds. The analysis suggests that the latter term is the dominant factor determining the relative chemical shifts, the most probable value of ΔX CC being near 7 × 10-30 cm3 molecule-1. The relative shifts of the methyl and methine protons of meso and dl 2, 3-disubstituted butanes and axial and equatorial methyl groups in cyclohexane rings are discussed in relation to this value of ΔX CC.

Microwave Spectrum, Molecular Structure of Vinyl Cyanide and a Summary of CC, CH Bond Lengths in Simple Molecules

The microwave spectra of six isotopic species of vinyl cyanide (acrylonitrile) CH2CHCN have been investigated. From the rotational constants it is shown that the molecule is planar, and has the following structural parameters (exclusive of the CH2 group): r s ( C ≡ N )=1.163 7 A ,r s ( C − H )=1.086 3 A , r s ( C − C )=1.425 6 A ,∠ C = C − C =122 ∘ 37 ′ , r s ( C = C )=1.338 9 A ,∠ H − C − C =121 ∘ 44 ′ . The quadrupole hyperfine structure was interpreted according to the asymmetric top treatment leading to a value of eqQ = —4.21±0.04 Mc/sec for the quadrupole coupling constant along the C≡N bond. A table of the most accurate published values of CC and CH bond lengths is included. A graphical presentation of these results shows that the C–C, C=C, and C–H bond lengths vary linearly with the number of adjacent bonds.