The use of substitution groups to derive thermodynamical relations between the material constants of piezoelectric materials

It is shown how substitution groups can be used to derive relations between the material constants of an anisotropic homogeneous piezoelectric medium. The structure of these relations is explained by means of a general record and independent systems are found, the existence of which has a clear physical interpretation. The concept of substitution group is generalized and some important thermodynamic substitution groups are derived; the method can be applied without substantial changes to an arbitrary type of anisotropic homogeneous medium.     

The nuclear magnetic resonance of Co59 and hyperfine fields in Fe-Co alloy

The nuclear magnetic resonance of Co⁵⁹ in an Fe-Co alloy was studied for a concentration of 4 to 17% Co. The resonance frequency was found to be independent of the concentration in this range. This observation is discussed together with the experimentally found dependence of the hyperfine field of iron in this alloy on the concentration of Co [8]. Use is made of a band model for 3d electrons of iron, in which the Co atoms behave as impurities on which certain wave functions of the band are localized and other delocalized. The values obtained for the line width show the presence of a mechanism of broadening, dependent on 3d wave functions.     

On the existence of tetragonally deformed octahedrons in the cubic part of the system MnxFe3-xO4

The mean square amplitude of lattice vibrations has been measured in the cubic part of the Mn _x Fe_3-x O₄-system. The observed increase of the -value with increasing content of Mn ions in the system is interpreted as that, with gradual occupation of more and more octahedral sites by Mn³⁺ ions towards higher values ofx, the number of locally distorted Mn³⁺O ₆ ^2– octahedrons increases.     

Über konvexe Multiplikatoren bei Fourier-Reihen

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