NIKOLAĬ VASIL'EVICH FEDORENKO (Obituary)

Abstract

In a previous communication to the Society the occurrence of wireless echo doublets was described and was provisionally attributed to the influence of the earth's magnetic field on the dispersive properties of the ionosphere. A more extended study of the subject, which has included an experimental determination of the polarizations of the doublet-components, has confirmed this hypothesis. In South-east England, for ionospheric reflection at vertical incidence, the echo-component of lesser delay is, in general, of right-handed, and the component of greater delay of left-handed, circular polarization, but this temporal sequence should be reversed in the Southern Hemisphere, and in certain special circumstances in the Northern Hemisphere.

Specific heat study and Landau analysis of the phase transition in PbTiO3single crystals

“…The more strongly first-order character of the phase change in PbTiO 3 makes equation (3) applicable only in the monophasic tetragonal state below T 0 [20], as seen more clearly in the inset of the figure. However, extrapolation of the data in the linear range at 730 K T 750 K to ( C P /T ) −2 = 0 gives T * = (764 ± 2) K in agreement with the relation [19]…”

“…Figure 3 shows the plot constructed from the C P data and it was found that equation (3) holds well (R 2 = 0.999) over the interval τ = 0.013-0.049. This interval of τ is somewhat smaller than expected as compared with other perovskite crystals with displacive transitions lying closer to a mean-field tricritical point [19]. The more strongly first-order character of the phase change in PbTiO 3 makes equation (3) applicable only in the monophasic tetragonal state below T 0 [20], as seen more clearly in the inset of the figure.…”

“…The data are well described by a straight line (R 2 = 1) of slope 0.086 K −1 above 700 K. From this line it was found that T 0 = (748 ± 2) K, T t = (760 ± 2) K and (T t − T 0 ) = (12 ± 3) K. From T t determined in this way we may compute the entropy discontinuity to be S XS = (2.0 ± 0.1) J mol −1 K −1 . Alternatively, for a first-order transition, it is possible to obtain two relations between the Landau coefficients in equation ( 1) directly from the heat capacity data by expressing the temperature dependence of C P = T (δS XS /δT ) in the general form [14,19]:…”

Calorimetric Investigation of Tricritical Behavior in Tetragonal Pb(ZrxTi1−x)O3

“…It is difficult to continuously vary the relevant thermodynamic parameters with the accuracy needed to arrive precisely at the tricritical points (9). Microcrystalline features of the sample, such as chemical heterogeneity and/or lattice imperfections, may also depend on composition, and can exert a considerable influence on the nature of the transition (10). Perhaps for these reasons, there are significant discrepancies in the reported compositions at which the tricritical points occur.…”

Lattice energies and structural distortions in Pb(ZrxTi1-x)O3solid solutions

“…In the mean-field theory, a change in the order of the transition is predicted to occur subject to the influence of an external parameter only if higher-order elastic terms, electrostrictive terms, or both are included in the Landau potential [26], or alternatively, if the lower-order terms adopt sufficiently renormalized values with respect to a variation in chemical composition in mixed crystals [27]. The applicability of the Landau theory to transitions near mean-field TCPs in solids both with and without impurities has been discussed in general terms by several authors [28,29].…”