Laser induced photo-thermal resistance response (PTRR) of polyisoprene/nanographite (PN) composites was studied. An inverse character of photoresistance in comparison to semiconductor-like materials was observed: electrical resistance of the PN composite increases when the intensity of the laser radiation is increased. The observed response can be explained by the photo-thermal effect: if the temperature of the PN composite rises because of optical radiation absorption then the electrical resistance increases due to positive temperature coefficient of the composite. Theoretical explanation of the positive temperature coefficient effect in PN composites based on tunneling-percolation model is given.

X-ray diffraction, dynamical mechanical analysis and infrared reflectivity studies revealed an antiferrodistortive phase transition in EuTiO3 ceramics. Near 300K the perovskite structure changes from cubic Pm-3m to tetragonal I4/mcm due to antiphase tilting of oxygen octahedra along the c axis (a0a0c- in Glazer notation). The phase transition is analogous to SrTiO3. However, some ceramics as well as single crystals of EuTiO3 show different infrared reflectivity spectra bringing evidence of a different crystal structure. In such samples electron diffraction revealed an incommensurate tetragonal structure with modulation wavevector q ~ 0.38 a*. Extra phonons in samples with modulated structure are activated in the IR spectra due to folding of the Brillouin zone. We propose that defects like Eu3+ and oxygen vacancies strongly influence the temperature of the phase transition to antiferrodistortive phase as well as the tendency to incommensurate modulation in EuTiO3.

Behaviour of ferroelectric properties in Na1/2Bi1/2TiO3-CdTiO3 solid solutions correlates with dependence of lattice symmetry versus concentration of constituents. However, some overlapping is observed in concentration range close to the morphotropic phase boundary. The properties of dielectric permittivity, characteristic for relaxor ferroelectrics, diminish, if concentration of CdTiO3 increases, but it is not influenced by the change of crystallographic symmetry. The electromechanical properties are mostly pronounced in the range of cubic-tetragonal morphotropic phase boundary.

Thermal expansion and electromechanical properties are studied for compositions Na1/2Bi1/2TiO3-SrTiO3-PbTiO3, belonging to various locations in the phase diagram. The main purpose of the studies is to extend the range of physical properties, which characterise the relaxor state and could be used for comparison with other relaxors. Possibility to evaluate Burns temperature from thermal expansion is discussed. The obtained results are compared to the well-know relaxor ferroelectric PLZT.

The tensor of the elastic stiffness constants C-ij of potassium thiocyanate (KSCN) has been measured in the temperature range 290 K to 420 K, including the order-disorder phase transition at 415 K, by the ultrasonic pulse echo overlap method at frequencies f = 20 MHz. Using the measured values for C-ij the isothermal elastic constants C-ij(T) were calculated from the data on specific heat C-P and the thermal expansion coefficients alpha(i). It turns out that there is a huge difference between the ultrasonic and the isothermal elastic constants in the low symmetry phase. The ultrasonic elastic constants exhibit only small positive anomalies which are proportional to the square of the order parameter while the isothermal ones tend to diminish on approaching T,. Measurements of the elastic constants of KSCN at ultralow frequencies (f = 0.1 Hz-50 Hz) show two dispersion regimes. One is due to the isothermal-adiabatic crossover (between 0.1 Hz and 50 Hz) and the second (between 50 Hz and 20 MHz) results from the order parameter dynamics.

ABSTRACT Role of a La on the nature of phase transition in the PLZT x/85/15 is compared with the PLZT compositions of lower Zr/Ti ratio. Thermal dependence of the dielectric permittivity, thermal expansion and elastic modulus reveal sequential transfer from macroscopic ferroelectric to antiferroelectric and nonpolar state, if La concentration is increased. Diffused, from frequency independent thermal dependence of dielectric permittivity for compositions in certain La concentration range above 4 at% coexist with the well expressed phase transition between paraelectric and antiferroelectric phases.

Carbon nanotubes offer attractive possibilities for developing new sensors because of superior mechanical and electrical properties. So far most studies relate the mechanical deformation to the change of nano-scale electrical properties. We present an attempt to use the multi-wall carbon nanotubes (MWCNT) to develop a new material for sensing macro-scale strain. Polymer composites containing dispersed nano-size particles, for example, polyisoprene - multi-wall carbon nanotube composites (PMCNTC) were prepared by treatment of the composite matrix with chloroform providing an increase of mobility and better dispersion of the nano-particles within the matrix. MWCNT with a small amount of solvent was carefully ground in a china pestle before adding to the polyisoprene matrix. Both the polyisoprene matrix solution and concentrated MWCNT product were mixed in a mixer with small glass beads at room temperature for 15 min. The product was dried at 40 °C for over 12 h and vulcanized under high pressure at 160 °C for 20 min. PMCNTC shows attractive tensile and compressive strain sensing properties. A mechanism of sensing effects is being investigated.

Analysis of conductivity and dielectric permittivity as functions of applied AC frequency and features responsible for the giant tenso‐resistance effect in polyisoprene‐extraconductive carbon black nanoparticles composites are presently reported. The experimentally obtained results are in good agreement with the mechanism of inter‐cluster polarisation. Some deviation from the statistical percolation theory at carbon concentrations above the percolation threshold is discussed.

Data obtained by dielectric spectroscopy reveal a strongly polydispersive, non-Debye dispersion appearing in potassium dihydrogen phosphate on cooling below the paraelectric-ferroelectric phase transition temperature Tc. Characterized by a nearly frequency-independent dielectric loss and a real part of the permittivity decreasing in an almost linear way with frequency on a logarithmic scale, the corresponding relaxation mechanism is discussed in terms of dielectric contributions of elastic domain walls weakly pinned on quenched disorder.

The elastic dynamics of AgNa(NO2)(2) crystals around the proper ferroelectric phase transition at T-C=38degreesC was investigated by ultrasonic (f=10 MHz) and dynamic mechanical analysis (f=0.6-50 Hz) techniques . The system represents a unique example of a ferroelectric crystal with extremely slow dielectric relaxation. Due to this reason it reveals a substantially different elastic behavior in megahertz and hertz frequency regions. We describe our data using a phenomenological model that includes both the effect of order parameter (polarization) relaxation with a characteristic time tau(p) and thermal (entropy) relaxation with a characteristic time tau(th).

Kim and Kim [Phys. Rev. B 59, 13 509 (1999)] have studied the frequency dependence of the complex permittivity of ${\mathrm{KH}}_{2}{\mathrm{PO}}_{4}$ and ${\mathrm{RbH}}_{2}{\mathrm{PO}}_{4}$ in the ferroelectric phase. In the low-frequency regime $(fl10 \mathrm{kHz})$ they found a dispersion consisting of at least three distinctive components. Considering the temperature dependence of those relaxational modes they claim that each of them is associated with domain wall motion, and not with a heat diffusion central peak (HDCP). The aim of this Comment is twofold: First we want to demonstrate the importance and influence of the ac measuring field on the dielectric properties, in particular in the temperature range $Tl{T}_{f}=100 \mathrm{K}l{T}_{c}$ of domain freezing. Second, by investigating the dielectric nonlinearity in the limit of small ac fields we exclude HDCP contributions in the low-frequency part of the spectrum.

Kim and Kim [Phys. Rev. B 59, 13 509 (1999)] have studied the frequency dependence of the complex permittivity of ${\mathrm{KH}}_{2}{\mathrm{PO}}_{4}$ and ${\mathrm{RbH}}_{2}{\mathrm{PO}}_{4}$ in the ferroelectric phase. In the low-frequency regime $(f<10 \mathrm{kHz})$ they found a dispersion consisting of at least three distinctive components. Considering the temperature dependence of those relaxational modes they claim that each of them is associated with domain wall motion, and not with a heat diffusion central peak (HDCP). The aim of this Comment is twofold: First we want to demonstrate the importance and influence of the ac measuring field on the dielectric properties, in particular in the temperature range $T<{T}_{f}=100 \mathrm{K}<{T}_{c}$ of domain freezing. Second, by investigating the dielectric nonlinearity in the limit of small ac fields we exclude HDCP contributions in the low-frequency part of the spectrum.

The dielectric, elastic and electromechanical properties, electrocaloric effect and thermal expansion of poled and depoled Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)O-3 samples are presented to evaluate the nature of polar phases existing in the solid solution above room temperature. The Kittel's free energy expansion is used to explain some essential features of physical properties.

Field induced deformation and electrocaloric effect are investigated in the vicinity of phase transition at 163 degrees C. The sharp increase of electrostriction below T-C is explained by the field induced ferroelectric to antiferroelectric phase transition. The antiferroelectric phase appears and remains stable below T-C in the absence of field. Elastic compliance and thermal expansion as functions of temperature are studied.

The (39)K1/2 --> -1/2 NMR angular rotation patterns in KSCN show no symmetry change on going through T-c. We have directly determined with N-14 NMR the SCN head-tail flipping rate. The results show that the absence of a symmetry change in K-39 angular rotation patterns is due to the fact that the time scale for the SCN fluctuations is much longer than the characteristic time scale of this experiment. The same is true for the diffuse neutron scattering data where both above and below T-c the SCN groups appear ordered and static and disorder is restricted to domain boundaries. KSCN thus seems to be the first known example where a structural phase transition can be observed in the slow motion and not in the fast motion regime and where a dynamic breaking of the symmetry of the high temperature phase takes place.