Broadband dielectric spectroscopy of Pb-based relaxor ferroelectric (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 with intermediate random fields

This work is devoted to the investigation of the broad band dielectric spectra of 0.83PbMg1/3Nb2/3O3-0.17PbTiO3 (PMN-17PT) single crystals which have intermediate random fields. The necessity to understand the impact of random fields for the phase transition in heterogeneous perovskite oxides is of central importance. The thorough studies of dielectric properties revealed that the structural phase transition in PMN-17PT has a very complex dynamics. The temperature dependences of dielectric permittivity show that this material has features characteristic of polar nano regions and order-disorder phase transition dynamics. We speculate that this is the fingerprint of the phase transition in such heterogeneous perovskite oxides

Lattice dynamics and electromechanical response in disordered perovskites

Perovskite oxides with a charge/site disorder possess superior dielectric, ferroelectric and electromechanical properties. These functional properties are relevant for various technological applications, yet still there are many scientific challenges in the field. The phase diagrams of complex perovskites have an exotic crossover from relaxor to normal ferroelectric behaviour. The mechanism of the phase transitions in such phase diagrams are not well understood and remains one of the forefront problems in the field of ferroelectricity. In this work, several perovskite oxide systems with a charge disorder in the different site of the perovskite lattice are investigated. The lattice dynamics of these systems are thoroughly studied by broadband dielectric, IR and Raman spectroscopic studies. The studies revealed the evolution of (nano)domains and their contribution to the macroscopic properties. It revealed that the phase transitions and dielectric anomalies can be associated to the thermal evolution of the central (relaxation) mode. The electromechanical properties in macroscopic and microscopic scale is also reported. It was concluded that the complex local polar patterns contribute to the macroscopic reponse in a same manner although they are different at the nanoscale

Gardelės dinamika ir elektromechaninis atsakas netvarkiuose perovskituose

Perovskite oxides with a charge/site disorder possess superior dielectric, ferroelectric and electromechanical properties. These functional properties are relevant for various technological applications, yet still there are many scientific challenges in the field. The phase diagrams of complex perovskites have an exotic crossover from relaxor to normal ferroelectric behaviour. The mechanism of the phase transitions in such phase diagrams are not well understood and remains one of the forefront problems in the field of ferroelectricity. In this work, several perovskite oxide systems with a charge disorder in the different site of the perovskite lattice are investigated. The lattice dynamics of these systems are thoroughly studied by broadband dielectric, IR and Raman spectroscopic studies. The studies revealed the evolution of (nano)domains and their contribution to the macroscopic properties. It revealed that the phase transitions and dielectric anomalies can be associated to the thermal evolution of the central (relaxation) mode. The electromechanical properties in macroscopic and microscopic scale is also reported. It was concluded that the complex local polar patterns contribute to the macroscopic reponse in a same manner although they are different at the nanoscale

Ultrasonic properties of composites of polymers and inorganic nanoparticles

The temperature dependencies of ultrasonic velocity and attenuation were measured in composites of inorganic nanoparticles with two types of polymers, poly(urea) elastomer with inorganic Mo6S4I6 nanowires and poly(ϵ-caprolactone) (PCL) with Mo6S3I6 nanowires. Below room temperature large ultrasonic relaxation attenuation maxima and velocity dispersion were observed. It was found that the attenuation peak in the elastomer shifted to higher temperature after doping with nanoparticles and this behavior was related to the shift of glass transition temperature. The ultrasonic attenuation data was fitted to a relaxation equation with a single temperature dependent relaxation time. The thermal activation energy of the relaxation process, which was calculated from ultrasonic data, was found to increase in the poly(urea) elastomer doped with MoSI nanowires. The low temperature ultrasonic velocity increased in the poly(urea) with nanowires added and is determined by the increase in elastic modulus. Similar ultrasonic behavior was obtained for PCL composites with inorganic MoSI nanowires. In this case, the increase in elastic modulus was smaller in comparison to the composites of poly(urea) and nanowires. Therefore, reinforcement of PCL was less pronounced

Ultrasonic studies of polymer composites with inorganic nanotubes

The temperature dependencies of longitudinal ultrasonic attenuation and velocity in several groups of new polyurea elastomers and poly(ε-caprolactone) composites were measured. In region of the glass transition the large ultrasonic attenuation maxima were observed. These peaks have relaxation behavior and can be approximated by temperature dependant relaxation time described by Arrhenius equation. The position of ultrasonic attenuation maxima and activation energy of relaxation process depends on the structure of the polyurea network. The ultrasonic relaxation peak in poly(ε-caprolactone) is also related to glass transition. The influence of inorganic nanotubes and nanowires in polyurea elastomers and poly(ε-caprolactone) is also discussed

Effect of Mo6S3I6 nanowires on the dielectric properties of poly(ϵ-caprolactone)

The broadband dielectric properties of composites of poly(ϵ-caprolactone) (PCL) and Mo6S3I6 (MoSI) nanowires at loadings up to 5 wt% were investigated. Three different relaxations were observed for these composites, two relaxations are associated with the polymer matrix and the lower temperature relaxation originates from the nanowires. No significant increase in a.c. conductivity was observed when the nanowires were introduced to the polymer. The only impact of nanowires on the polymer was seen at lower temperatures (T < 100 K), where another relaxation occurs when the concentration of nanowires was increased. Temperature dependency of relaxation time follows Arrhenius behavior. Activation energy was determined and it is concentration independent

Temperature and frequency dependence of the dielectric and piezoelectric response of P(VDF-TrFE)/CoFe2O4 magnetoelectric composites

CoFe2O4 nanoparticles embedded on polyvinylidene fluoride (PVDF) matrix shows suitable propertied for practical application as piezoelectric and magnetoelectric transducers. Essential for these applications is the knowledge about the dielectric, ferroelectric and piezoelectric responses of the multiferroic films at high frequencies and low temperatures. This work reports on the effect of ferrite content, temperature and frequency on the dielectric, ferroelectric and piezoelectric responses of magnetoelectric CoFe2O4 nanocomposites. It was observed that for frequencies lower than 100 kHz, no substantial differences are detected on the ɛ’ and ɛ’’ values from composites with CoFe2O4 contents ranging from 5 to 11 wt.%. For higher frequencies (100 kHz - 250 MHz) and at temperatures ranging from 150 K to 400 K the same trend is observed, the ɛ’ and ɛ’’ values are being higher for the composite with 5 wt.% of ferrite content and lower in the composites with 11 wt.%, indicating that after a critical filler loading, the e CoFe2O4 nanoparticles lead to a decrease the dielectric response of the composites at higher frequencies. For all composite compositions increasing temperature leads to lower coercive fields and higher piezoelectric and polarization values.FCT-Fundação para a Ciência e Tecnologia for financial support under grant SFRH/BPD/96227/2013. SLM thanks financial support from the Basque Government Industry Department under the ELKARTEK Program and the Diputación Foral de Bizkaia for finantial support under the Bizkaia Talent program; European Union’s Seventh Framework Programme; Marie Curie Actions – People; Grant agreement nº 267230info:eu-repo/semantics/publishedVersio

Implications of acceptor doping in the polarization and electrocaloric response of 0.9Pb(Mg1/3Nb2/3)O-3-0.1PbTiO(3) relaxor ferroelectric ceramics

In ferroelectrics, the effects of acceptor doping on electrical and electromechanical properties, often referred to as the "hardening" effects, are commonly related to domain-wall pinning mechanisms mediated by acceptor-oxygen-vacancy defect complexes. In contrast, the hardening effects in relaxor ferroelectric materials are complicated by the nano-polar nature of these materials, the associated dynamics of the polar nano-regions and their contribution to polarization, and the characteristic freezing transition between the ergodic and the non-ergodic phases. To shed light on this issue, in this study, we investigate the role of the acceptor (Mn) doping on the temperature-dependent broadband dielectric permittivity, high-field polarization-electric-field (P-E) hysteresis and electrocaloric (EC) response of 0.9Pb(Mg1/3Nb2/3)O-3-0.1PbTiO(3) (PMN-10PT) relaxor ferroelectric ceramics. The results suggest strong pinning effects, mediated by the acceptor-oxygen-vacancy defect complexes, which manifest similarly both in the ergodic and in the non-ergodic phases of PMN-10PT as revealed by the doping-induced suppression of the frequency dispersion of the permittivity maximum and pinched high-field hysteresis loops. In addition to these pinning effects, the Mn doping reduces the freezing temperature (T-f) by similar to 50 degrees C with respect to the undoped PMN-10PT. This is reflected in the EC response, which becomes less temperature dependent, making defect engineering a valuable approach for designing EC materials with an extended operational temperature range