Single crystals of the solid solution tris-sarcosine calcium chloride1-xbromidex were grown for O ≤ x ≤ 1. TSCC shows a second-order ferroelectric transition at 132 K whereas TSCB possesses no ferroelectric phase. The concentration dependence of the transition temperature obtained by low frequency permittivity measurements is described by the empirical relation Tc(x) = Tc(o) (1 - x/xcr)½. No ferroelectric transition was observed above the critical concentration xcr = 0.74. Above Tc all ferroelectric samples show a Curie-Weiss behaviour for about 10 K. For x near 0.5 the quality of the crystals is lowered and the permittivity peak is broadened.

Dielectric, structural and nuclear magnetic resonance (nmr) properties of TSCC point at a ferroelectric transition of the order-disorder type, which may be triggered by the dynamics of the protons in the hydrogen bonds. From electron paramagnetic resonance (epr) experiments on TSCC: Mn2+ a relation between fine structure and the time average of the quasi spin variables has been found. Electron spin-echo (ese) measurements of the transverse relaxation time and epr line width investigations near transition temperature are consistent with an anisotropic Ising model of the relaxation type. The static rotation angle of the fine structure tensor correlates with the macroscopic order parameter. Its temperature dependence yields an effective critical exponent whose variation may be interpreted as the influence of order parameter fluctuations on the order of the phase transition.

In BCCD the EPR probes Mn2+, VO2+, and as an irradiation centre the radical N(CH3)(3) monitor the incommensurate modulation. Interesting results on the influence of defects on the order parameter were obtained using Mn2+ taking into account the influence of second-order effects on the EPR line shifts.

By a combination of X-band and e-band ESR investigations it was possible to distinguish between effects of first and second order in the critical behavior, which are influenced in different ways by the dynamics of the order-parameter fluctuations. The theoretical analysis is based on a Fourier expansion of the ESR fine-structure elements in terms of the harmonics of the incommensurate modulation. Second-order perturbation theory for the evaluation of the ESR spectra was applied. The splitting between thr edge singularities should show a temperature dependence given by the superposition of two different critical contributions: Delta B-ES=a(T-i-T)(<(beta)over bar>)+b(T-i-T)(2 beta). The second contribution depends on the strength of the external magnetic field. This could be clearly revealed in the comparison between Q- and X-band measurements. The influence of the Mn content c(Mn) or of the gamma-irradiation dose c(gamma) on the splitting of the edge singularities was analyzed. [S0163-1829(98)03929-0].

Low temperature heat capacity measurements (0.6<T<20 K) have been performed in a large umpoled single crystal of ferroelectric trisarcosine calcium chloride (TSCC). A Debye temperature Theta(D)(c) similar or equal to 384 K is obtained. As previously reported in other ferroelectric crystals, a contribution in excess of T-3 Debye one, is observed at the lowest temperatures.

In calcium modified lead titanate ceramics with a Ca/Pb ratio between 0.01 and 0.5 were estimated at room temperature the lattice parameters by X-ray diffraction and the transition temperatures by dielectric and thermal dilatational measurements. The change in the tetragonality (c/a) - 1—which is related to the order parameter—with the Ca concentration and temperature is explained within the framework of the model of coupled anharmonic oscillators in high temperature approximation with only two fitting parameters. The temperature dependence of the lattice parameters for a sample with 24% Ca reveals a second order transition near to tricritical behavior. Key Words: Perovskite ceramics model of coupled anharmonic oscillators.

XRD, magnetic susceptibility, and EPR studies are reported for the BaCuO2+x compound in both the oxygenated and nonoxygenated phases. The XRD analysis has shown essential differences in the disordered part between the oxygenated and the nonoxygenated samples. The magnetic susceptibility measurements have shown strong ferromagnetic intracluster interactions among copper ions in the ordered part of the compound. At low temperature, antiferromagnetic intercluster interactions mediated by the disordered part predominate. EPR measurements in both phases have revealed a spectrum of Cu2+ ions, in orthorhombic local symmetry, which is attributed to copper ions in the disordered part. An intense exchange-narrowed EPR line has also been observed in both phases, which is ascribed to the copper clusters in the ordered part. The temperature dependence of the intensity and linewidth of this line is consistent with the bulk magnetic behaviour. At low temperature, the divergent behaviour of the EPR parameters indicates that antiferromagnetic ordering may occur. Additionally, it was found that the EPR spectra are essentially influenced by thermal treatment and the ordering of the oxygen atoms in the disordered part of the compound.

Within the framework of the model of coupled anharmonic oscillators a ferroelectric solid solution is described with only a few parameters. In high-temperature approximation a linear relation between the square of the order parameter and the transition temperature is obtained. This is illustrated by an application to several modified lead titanate ceramics, the linear relation between transition temperature and tetragonal lattice deformation is verified. For tris-sarcosine calcium chloride (bromide) (TSCC/B) at very low temperatures the expected deviation from the classical behaviour is seen.

A simple physical model is used to interpret the line shape of the Mn2+ EPR spectrum of the first incommensurate phase of betaine calcium chloride dihydrate and it is discussed in comparison with other models. Furthermore, the critical behavior of BCCD at the normal to incommensurate phase transition on the basis of our model is investigated. The influence of the Mn2+ impurities on the phase sequence of BCCD is investigated by dielectric measurements.

physica status solidi (b)Volume 181, Issue 2 p. K69-K72 Short Note EPR Spectra of Polycrystalline REBaCuFeO5 (RE = Eu, Y, Yb) N. Guskos, N. Guskos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorV. Likodimos, V. Likodimos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorJ. Kuriata, J. Kuriata Institute of Physics, Technical University of Szczecin Search for more papers by this authorH. Metz, H. Metz Fachbereich Physik der Universität Leipzig Search for more papers by this authorW. Windsch, W. Windsch Fachbereich Physik der Universität Leipzig Search for more papers by this authorM. Wabia, M. Wabia Institute of Physics, Technical University of Szczecin Search for more papers by this authorC. Mitros, C. Mitros Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this authorD. Niarchos, D. Niarchos Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this author N. Guskos, N. Guskos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorV. Likodimos, V. Likodimos Department of Physics, Institute of Solid State Physics, University of Athens Search for more papers by this authorJ. Kuriata, J. Kuriata Institute of Physics, Technical University of Szczecin Search for more papers by this authorH. Metz, H. Metz Fachbereich Physik der Universität Leipzig Search for more papers by this authorW. Windsch, W. Windsch Fachbereich Physik der Universität Leipzig Search for more papers by this authorM. Wabia, M. Wabia Institute of Physics, Technical University of Szczecin Search for more papers by this authorC. Mitros, C. Mitros Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this authorD. Niarchos, D. Niarchos Institute of Material Science, N.C.S.R. “Democritos”, Athens Search for more papers by this author First published: 1 February 1994 https://doi.org/10.1002/pssb.2221810233Citations: 5 Panepistimiopolis, GR-15784 Zografos, Athens, Greece. Al. Piastow 17, PL-70-310 Szczecin, Poland. Linnéstr. 5, D-04103 Leipzig, Federal Republic of Germany. Aghia Paraskevi, GR-15310 Attikis, Athens, Greece. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References 1 M. Pissas, C. Mitros, V. Psycharis, G. Kalias, A. Simopoulos, A. Kostikas, D. Niarchos, C. Xristiadis, and K. Prassidis, Proc. VII Hellenic Solid State Physics Conf., 20 to 22 Sept. 1991, Thessaloniki (Greece) (p. 424). Google Scholar 2 L. Er-Rakho, C. Miceli, P. Lacorve, and B. Ravean, J. Solid State Chem. 73, 531 (1988). 10.1016/0022-4596(88)90141-7 CASWeb of Science®Google Scholar 3 C. M. Brodbeck, J. non-crystall. Solids 40, 305 (1980). 10.1016/0022-3093(80)90108-8 CASWeb of Science®Google Scholar 4 D. J. Newman and W. J. Urban, J. Phys. C 5, 3101 (1972). 10.1088/0022-3719/5/21/015 CASWeb of Science®Google Scholar 5 A. Abraham and B. Bleaney, Electron Paramagnetic Resonance of Transition Ions, Clarendon Press, Oxford 1970. Google Scholar Citing Literature Volume181, Issue21 February 1994Pages K69-K72 ReferencesRelatedInformation

Experimental data on the mixed system Pb(1−x)CaxTiO3 for 0 ≤ x ≤ 0.40 (molar concentration) indicate a trend from a clearly first order transition at x = 0 to a second order (tricritical point) transition at x ≃ 0.40, characterized by a decrease with x of the thermal hysteresis. ΔT = T* −T c, where T* is the transition temperature and T c the extrapolated Curie temperature. An analysis of these data in terms of the generalized effective field approximation (E eff = E + βP + γP 3 + δP 5 …) for the mixed system leads to a quantitatively satisfactory prediction of the tricritical point concentration, x c ≃ 0.40, from data pertaining to the pure system (PbTiO3) alone.

Oxygenated and non-oxygenated LaBaSrCU3O6+x ceramics in the tetragonal phase are studied using X-ray, EPR, and magnetic measurements. A Meissner signal for the oxygenated sample corresponding to almost perfect diamagnetism is measured below 35 K. However, EPR data indicate that at least some parts of the sample become superconducting already below 62 K. Magnetic susceptibility of the non-oxygenated sample exhibit a significant paramagnetic contribution attributed to Cu(1) ions ferromagnetically coupled to the Cu(2) planes.

Relevant data on Tris-Sarcosine Calcium Chloride (TSCC), including temperature dependent data of spontaneous polarization (P = 0.27 muC/cm2), dielectric permittivity (Curie constant at T > T(c) C = 59 K, and Curie temperature T(c) = 125.4 K) and specific heat (DELTAC(p) = 0.27 x 10(6) erg/K cm3, specific heat jump at T = T(c) after discounting for logarithmic corrections) have been analyzed within the framework of the effective field approach to ferroelectric transitions, resulting in N = 1.01 x 10(21) dipoles/cm3 and mu = 0.80 x 10(-18) esu cm, in good agreement with microscopic observations. Consideration of quadrupolar (g not-equal 0) and octopolar (h not-equal 0) contributions to the effective field improve the theoretical fit to (P(s)/P(so)) vs. (T/T(c)) data.

EPR investigations on Mn2+ doped betaine calciumchloride dihydrate show that Mn2+ incorporated at Ca2+ sites is a good indicator for the modulated phases of BCCD. At low temperatures the existence of a nonmodulated phase with low symmetry was confirmed. ENDOR measurements show that a radical arises at gamma irradiation of BCCD with nearly sp2 hybridization and two states.

Abstract Mizuno et al. developed a jumping model to explain the nonlinear decrease of the phase transition temperature in the mixed crystals (NH4)2(1-x)K2xPb[Cu(NO2)6] with 0 ≦ x ≦ 1. Their implications and results are compared with model parameters and with the results of calculation within the Ising model with transverse field. It comes out that the assumption of a temperature independent transient time in the jumping model corresponds to the admission of tunneling in the Ising model.

EPR investigations on Mn2+-doped calcium chloride dihydrate monitor the rich variety of commensurate and incommensurate phases. The line shape in the first incommensurate phase is interpreted by assuming a superposition of one line with two edge singularities and an unshifted line. In the ferroelectric phase below 46.5 K the mirror symmetry is lost and the fine structure tensor is tilted by ±5°.

The EPR spectra of perovskite ceramics of Gd0.5RE0.5Ba2Cu3O7-delta type (RE = La, Pr, Nd, Sm, Eu, Dy, Ho, Y, Er, Tm, Yb, and Lu) in tetragonal (non-HTC) phase are investigated as a function of temperature in the range 40 to 3 K. A signal arising from the isotropic exchange interaction of coupled pairs of Cu2+ ions is detected. The intensity of this signal is strongly dependent on the RE ions and its g-factor varies with temperature. Magnetic measurements show the existence of ferromagnetic anomalies at these low temperature. In the orthorhombic phase, these materials exhibit a superconducting phase transition in the range of 85 to 95 K, apart from the samples with La ions where a T(c) almost-equal-to 69 K is found and the samples with Pr ions where a superconducting state can not be observed.