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The demand for high dielectric constant materials and high energy density capacitors has rapidly increased in recent years due to the continuous and rapid development of the electronic industry and the need to store electrostatic energy more efficiently. The introduction of ferroelectric inclusions in a polymeric matrix enables the effective dielectric constant of the composite to be significantly increased while preserving the high breakdown field typical of polymers, thus improving the stored energy density. By varying the size, shape and volume fraction of the inclusions, the dielectric properties of the composite can be tailored, as a consequence of the alteration of the electric field distribution inside the material. A further approach for the modification of the electric field in the composite is coating the particles used as inclusions with an oxide layer with a different dielectric constant. In this work we have fabricated polyvinyldene fluoride (PVDF) composites containing 30 vol.% BaTiO3@AO2 (A = Si, Ti) particles. Barium titanate particles with a diameter of ?100 nm were synthesized using a hydrothermal-like method and coated with a thin shell (10 nm) of SiO2 or TiO2 by means of colloidal chemistry methods. The composites were prepared by solution casting and subsequent compression moulding. Reference composites were prepared by the same process using uncoated BaTiO3 particles. In order to understand the effect of interfacial modification by coating of the filler, the dielectric properties of the composites (dielectric constant and loss tangent) were measured at different frequencies (1 - 106 Hz) in the temperature range 25-150 °C. The coating results in a significant modification on the effective permittivity, which is mainly determined by the value of its dielectric constant. To gain insight into the role of the coating layer, the electric field distribution and the effective dielectric constant were calculated for the different composites using a 3D finite element modelling and compared to experimental results. This study provides some guidelines for tuning the dielectric properties of ferroelectric PVDF-ceramic composites. Acknowledgements: This work was funded by Fondazione Bancaria Compagnia di San Paolo, under the framework of the Project "Polycom".

The high relative dielectric constant (?r = 2000-5000) and low losses (?1%) of ferroelectric barium titanate, BaTiO3, has made it the most widely used dielectric ceramic material in the electronic industry for the fabrication of multilayer ceramic capacitors, which are used in most electronic circuits, with an annual production of 2000 billion of devices. Owing to the strong temperature dependence of the dielectric constant, BaTiO3 cannot be used in pure form, but its properties have to be properly modified by the incorporation of suitable dopants. Pure BaTiO3 has 4 crystallographic variants, depending on the temperature. The substitution of Ti4+ (r = 0.605 Å) with a homovalent ion in BaTiO3 ceramics, with formation of BaMxTi1-xO3 (M = Sn, Hf, Zr, Ce) solid solutions, modifies the polar order, with increasing x, from conventional ferroelectric to a so-called relaxor behaviour for high substitution levels via a diffuse transition. Irrespective of M, with increasing x the three phase transitions merge at a tricritical point (xp, Tp), TCP, the so-called pinched transition, where the four polymorphs coexist. For x > xp, the system then directly transforms from the ferroelectric R phase to the C paraelectric phase with a diffuse transition. BaMxTi1-xO3 solid solutions have gained large attention for applications. In fact, they show properties such as a very high (1-2·104) and stable dielectric constant around room temperature, large dielectric tunability and improved piezoelectric activity, of potential interest for a number of applications, such as, respectively, high permittivity dielectrics, microwave devices for telecommunications, and lead-free piezoelectric sensors, actuators and energy harvester. Recently it was also theoretically predicted and experimentally observed for M = Sn, Hf, Zr, that for specific compositions corresponding to the coexistence of different phases, such as the one close to the TCP, BaMxTi1-xO3 develops a large electrocaloric response, that could be used in cooling devices. We present an extensive investigation of BaMxTi1-xO3 (M = Zr, Ce) over a broad range of compositions, combining macroscopic property measurements and average structure information (electric properties, DSC analysis and high resolution XRD) with the local structure analysis (PDF analysis and Raman spectroscopy). Among the four M ions, Ce4+ substitution is the less studied, although it is the largest ion and thus a model system to study the effect of strain on the onset of relaxor behaviour. By comparing our results with the available literature, some general conclusions can be drawn on the origin of relaxor behaviour for the BaMxTi1-xO3 system. In fact, the compositions corresponding to the tricritical point and the ferroelectricto- relaxor crossover in BaMxTi1-xO3 are nearly independent on M, suggesting that, irrespective of the M4+ radius, a critical number of Ti-O-Ti bonds has to be broken before a new "state" is established.

Polymer-ceramics nanocomposites are spreading in the field of printed wiring boards and microelectronic packaging because they provide an ideal solution to combine the good dielectric and electrical properties of the ceramic filler with the resistance to high electric field, the low-temperature processability and the suitable mechanical properties of the polymer matrix [1]. The dielectric properties of these composites can be in principle tunable by changing amount, dimension and type of filler. In this work, 0-3 connectivity nanocomposites based on poly(vinylidene fluoride) (PVDF) and containing 30 vol% of ceramic inclusions were prepared by solution casting followed by compression moulding. In particular, BaTiO3 nanoparticles were employed as such or coated with shells of SiO2 or TiO2 at different thickness in order to study the influence of surface coating on the final properties of the composites.

BaTiO3 perovskite and its solid solutions are nowadays the most used ferroelectric materials, being them environmental friendly and with excellent properties. Among the various possible solid solutions with homovalent substitution at Ti site (BaTi1-xMIVxO3), only BaTi1-xZrxO3 was studied extensively from the structural point of view [1]. Other substitutions can be interesting: in particular, the one with cerium, BaCexTi1-xO3 (BCT), which presents a large difference in size between Ti and Ce ions. Therefore, in this work, BCT with different Ce amount (x=0.02-0.20) and various particle sizes (from 80-160 nm to 5 um) was deeply explored both on the average and on the local structure by means of traditional Rietveld method and Pair Distribution Function. BCT in its ceramic form (grain size: 1 to 5 um) presents a polar behaviour variation from conventional ferroelectric to relaxor via diffuse phase transition (DPT) [2, 3]. As the particle size is reduced, the so called "size effect" takes over, with larger variations in the electric properties with composition. It is well known that ferroelectricity is related to titanium displacement within the octahedra, and our Rietveld analysis results find a good agreement between measured material properties and titanium offcenter values in the ceramic materials. The progressive suppression of the spontaneous polarization with x and the cubic phase stabilization is related to the disruption of the correlated Ti displacements engendered by the large Ce4+ incorporated at the octahedral site [4], and a complex model must be used for the local structure. All the described effects are generally more pronounced when the material presents a reduced particle size, as cerium content and reduced size cooperate in the extension of the cubic structure stability field, with respect to the corresponding micrometric materials. The distortions at the local level are therefore confirmed to be largely responsible for the ferroelectric properties of the BaCexTi1-xO3 perovskite, either in the micrometric or in the reduced size samples. [1] V. Buscaglia, S. Tripathi, V. Petkov, M. Dapiaggi, M. Deluca, A. Gajovic, Y. Ren, J. Phys. Condens. Matter 26 (2014), 065901. [2] V.V. Shvartsman, D.C. Lupascu, J. Am. Ceram. Soc. 95 (2012), 1. [3] G. Canu, G. Confalonieri, M. Deluca, L. Curecheriu, M.T. Buscaglia, M. Asandulesa, N. Horchidan, M. Dapiaggi, L. Mitoseriu, V. Buscaglia, Acta Mater. 152 (2018), 258. [4] G. Confalonieri, V. Buscaglia, G. Capitani, G. Canu, N. Rotiroti, A. Bernasconi, A. Pavese & M. Dapiaggi, J. Appl. Cryst 51 (2018), 1283.

The substitution of Ti4+ (r = 0.605Å) with a homovalent ion in BaTiO3 ceramics, with formation of BaMxTi1-xO3 (M= Sn, Hf, Zr, Ce) solid solutions, has gained large attention for applications as dielectric or piezoelectric materials. Ce4+ (0.87Å) is the largest among these M ions, thus BaCexTi1-xO3 is a model system to investigate the effects of local strain on macroscopic properties. We present an extensive investigation of BaCexTi1-xO3 over compositions in the x=0.02-0.30 range combining macroscopic property measurements and average structure information with the local structure analysis. By comparing our results with the available literature, especially regarding Zr and Sn substitution, some general conclusions can be drawn. In fact, the compositions corresponding to the tricritical point and the ferroelectric-to-relaxor crossover in BaMxTi1-xO3 are nearly independent on M, suggesting that, irrespective of the M4+ radius, a critical number of Ti-O-Ti bonds has to be broken before a new "state" is established.

The ability to tune and enhance the properties of luminescent materials (phosphors) is essential for optimizing the performance of devices and understanding the luminescence mechanisms. Eu3+ was used as a local structural probe for studying the impact of ferroelectric order and, more generally, of polar order on the photoluminescence of the model BaZrxTi1-xO3 perovskite (x = 0-1). The polar order evolves from long-range order typical of classic ferroelectrics (x = 0-0.15), via a diffuse transition behaviour (x = 0.15-0.25), to short-range order typical of relaxors (x >= 0.25) until the paraelectric state of BaZrO3 is achieved. The cooperative polar interactions existing in the lattice (x < 1) promote the off-centre displacement of Eu3+ determining a change of the lanthanide site symmetry and, consequently, an abrupt variation of the photoluminescence emission with temperature.

High-permittivity (high-k) polymer-ceramic composites with engineered nano-architecture meet the increasingly marked tendency towards a more rational and sustainable use of energy. They provide a smart solution to combine the good dielectric properties of the ceramic filler with the processability, flexibility and high breakdown strength of the polymer matrix [1]. In this work, 0-3 connectivity nanocomposites based on poly(vinylidene fluoride) (PVDF) and containing 30 vol% of ceramic inclusions were prepared by solution casting followed by compression moulding. BaTiO3 nanoparticles, both as synthesised and coated with a thin shell of a binary oxide (SiO2 or TiO2), were employed to understand the role of interfaces, shape and morphology of inclusions. A better insight of the correlation between composite microstructure and dielectric properties was gained by combining FEM simulation and experimental data.

In the present work, an alternative method to induce the formation of PVDF ? phase was proposed, exploiting a well-known technique widely used for the polymer processing: the compression molding. In particular, it was used a double step process (P2), which consists in preparing a plate of material (i.e. neat PVDF or composite) and then repressing it at high pressure and at a temperature lower than the PVDF melting temperature. As concerns the neat PVDF, the molding conditions were modified to investigate their influence on the final amount of electroactive phase(s) obtained. The impact of processing on dielectric and dynamic-mechanical properties of the PVDF films was also studied on a selected series of samples. PVDF-based composites containing different amount of ceramic particles (such as BaTiO3 and PZT), widely used in the field of energy harvesting, were then prepared by solvent casting or melt blending. Besides a single-step (P1) molding carried out on samples with completely molten PVDF, also the P2 process was applied to the composites in order to investigate its effect on their final properties. The ensuing samples were characterized from morphological, spectroscopic, dynamic-mechanical and dielectric point of views.

Ba0.85Ca0.15Ti0.90Zr0.10O3 (BCTZ) pseudobinary ferroelectric is one of the most promising BT-based materials for piezoelectric applications. In this work, a series of dense BCTZ ceramics with grain size larger than 1?m and uniform grain-size distribution were successfully prepared by the conventional solid-state reaction, and the grain-size effects on the structural, dielectric, ferroelectric and piezoelectric properties were explored in their un-poled and poled states. The ceramics were obtained by sintering solid state powders at different temperatures between 1400- 1500°C and times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 2 ?m for the samples sintered at 1400ºC/2h to 27 ?m for the samples obtained at 1500ºC /24h. The structural characterization was performed for monitoring the effect of grain size and field on the phase composition in BCTZ ceramics. The evolution of polar order and phase transitions with grain size has been studied using dielectric permittivity measurements at 20Hz- 2MHz between 25 and 150°C. Also, the piezoelectric properties at different poling conditions (poling temperature and electric field) were investigated and discussed according with ceramics grain size. Polarization vs. electric field (P-E) hysteresis loop study showed that exist a critical grain size (~ 9 ?m) for which the remnant and saturation polarisation is higher. The same critical size was obtained from dc-tunability investigation. In addition, we develop a mesoscale modelling (Monte Carlo with Finite Element Method calculations) to describe size effects on the low-field properties in BCTZ ceramics. The presented data provide a complete picture of the size effect dependence of functional properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics. Acknowledgements: The financial support of the PN III-P1-1.1-TE-2016-1951 is acknowledged

Rapporto finale sull'attività svolta per il progetto Polycom, nel periodo 18/03/2016 - 30/11/2018. L'attività si è svolta seguendo la programmazione dettagliata nel progetto allegato alla domanda di finanziamento. L'attività è stata concentrata sulla fabbricazione e caratterizzazione dei compositi PVDF-BaTiO3. L'attività effettuata nel periodo è sintetizzabile come segue: WP1) Sintesi di polveri di BaTiO3 con diversi diametri e rivestimento di tali particelle con ossidi binari nelle quantità richieste per la fabbricazione dei compositi nel WP3. WP2) Funzionalizzazione di particelle di BaTiO3 non rivestite e rivestite con derivati silanici. WP3) Fabbricazione di compositi PVDF-BaTiO3 tramite miscelazione nel fuso (melt blending) o filmatura da solvente (solvent casting). I film sono stati poi realizzati tramite stampaggio per pressofusione (pressure moulding). I film sono stati caratterizzati dal punto di vista della microstruttura, della tipologia di gruppi funzionali presenti, delle proprietà termiche. WP4) Misura delle proprietà dielettriche in funzione della frequenza e della temperatura effettuata su semplici capacitori preparati utilizzando i film prodotti nel WP3. Su alcuni compositi selezionati sono state effettuate misure in funzione del campo elettrico applicato. WP5) Simulazione FEM 3D delle proprietà dielettriche di compositi contenenti tre diversi tipi di particelle, non rivestite e rivestite con due ossidi binari, in funzione della frazione in volume delle inclusioni e dello spessore del rivestimento. WP6) Le attività principali hanno riguardato la messa a punto definitiva e l'aggiornamento del sito web, l'organizzazione di due meeting di progetto, la presentazione dei risultati per mezzo di comunicazioni a conferenze, la stesura di pubblicazioni scientifiche. In tutti i casi è stata data la dovuta visibilità alla Compagnia di San Paolo come ente finanziatore. Prot. CNR-ICMATE n. 3080 del 19/12/2018

According to the working programme, it is reported the production of dense ceramics by a conventional ceramic process. Powders of V-doped BaTiO3 and Yb-doped BaTiO3 were prepared by solid-state reaction. The powders were compacted by cold isostatic pressing and the resulting cylindrical pellets sintered in air and characterised with x-ray diffractometry and electron microscopy; samples density was measured as well.

BaZrxTi1-xO3 (BZT) solid solutions with perovskite structure show a series of phase transitions and a progressive evolution of ferroelectric order, from long-range typical of ferroelectrics....

Barium titanate, BaTiO3, owing to its high relative dielectric constant and low losses is the most widely used dielectric ceramic material in the electronic industry. The substitution of Ti4+ with a homovalent ion with formation of BaMxTi1-xO3 (M = Sn, Hf, Zr, Ce) solid solutions has gained large attention from both fundamental and application point of view. These materials are attractive for applications such as high energy density capacitors, tunable microwave dielectrics and electrocaloric effect-based cooling devices [1-3]. BaCexTi1-xO3 solid solution is a model system to investigate the effects of local strain fields, Ce4+ being a much larger ion (r = 0.87 Å, c.n. 6) than Ti4+ (r = 0.605 Å, c.n. 6), but while an abundant literature exists on the solid solutions in which Ti is substituted by Sn and Zr, the effect of the incorporation of Ce4+ at the Ti site has not been systematically investigated yet. This work is a comprehensive study of BaCexTi1-xO3: in fact, it combines macroscopic property measurements and average structure information with complementary techniques sensitive to the local structure, i.e. X-ray Pair Distribution Function analysis and Raman spectroscopy, to gain comprehensive insight on the structure-property relationships. BaCexTi1-xO3 ceramics have been investigated over a broad composition (x = 0.02 - 0.30, the upper limit being very close to the solubility limit) and temperature (100 - 400 K) range. The data provide a detailed picture of the BaCexTi1-xO3 system and a composition-temperature phase diagram will be proposed. [1] V. V. Shvartsman, D. C. Lupascu, J. Am. Ceram. Soc., 95, 1-26 (2012), [2] X. S. Qian et al., Adv. Funct. Mater., 24, 1300-1305 (2014), [3] V. Buscaglia et al., J. Phys: Condens. Matter, 26, 065901 (2014)

The demand for high dielectric constant materials and high energy density capacitors has rapidly increased in recent years due to the continuous and rapid development of the electronic industry and the need to store electrostatic energy more efficiently. The high breakdown field typical of polymers can be preserved while increasing the effective permittivity, if ferroelectric inclusions are embedded in the polymer matrix by forming a 0-3 connectivity composite, thus improving the stored energy density. The dielectric properties of the composite can be tailored by varying size, shape and volume fraction of the inclusions as well as the dielectric constant of the polymeric matrix, thus altering the electric field distribution inside the material. Moreover, the distribution of the electric field can be modified by coating the particles used as inclusions with an oxide layer with a different dielectric constant. In this work we have fabricated poly(vinylidene fluoride) (PVDF) composites containing 30 vol.% BaTiO3@AO2 (A = Si, Ti) particles and measured their dielectric properties. Barium titanate particles with a diameter of ?100 nm were synthesized using a hydrothermal-like method and coated with a thin shell (?10 nm) of SiO2 or TiO2 by means of colloidal chemistry methods. The composites were prepared by solvent casting followed by compression moulding. The dielectric properties of the composites (permittivity and loss tangent) were measured at different frequencies and several temperatures. The coating results in a significant modification of the effective permittivity, which is mainly determined by the value of its dielectric constant. To gain insight into the role of the coating layer, the electric field distribution and effective dielectric constant were calculated for the different composites using a 3D finite element modelling and compared to experimental results. Acknowledgement Work carried out in the framework of Project Polycom (IDROL:10359) funded by Fondazione Bancaria Compagnia di San Paolo.

Polymer-based composites are very attractive for advanced applications in the field of energy harvesting, storage and conversion. For instance, the introduction of high-permittivity ceramic particles into a polymer matrix, characterized by high breakdown field, leads to dielectric materials able to store large amounts of energy while maintaining desirable properties of the polymer, such as processability and flexibility. In particular, poly(vinylidene fluoride) (PVDF) is widely used as matrix due to its higher dielectric permittivity (?10), compared to other polymers, and its capability to crystallize in five different polymorphs, some of which possess a neat moment dipole. In this work 0-3 connectivity PVDF-based composites containing 30 vol% ferroelectric BaTiO3 (BT) ceramic inclusions were prepared by solution casting followed by compression molding, properly adjusting the processing conditions in order to induce the formation of the electro-active ? polymorph of PVDF. Three different compression molding methods were employed for realizing PVDF-BaTiO3 composites: the most promising procedure was then used for the preparation of composites containing modified, i.e. core-shell and/or functionalized, BT nanoparticles. All nanoparticles were characterized by FTIR and TEM. A thorough characterization was performed on the composites to investigate the influence of processing conditions and of filler type on the resulting dielectric properties, taking into account PVDF polymorphism and particles dispersion within the polymer matrix.

BaTiO3-based ferroelectric ceramics show interesting properties such as high dielectric constant, low losses, high hydrostatic piezoelectric coefficient and PTCR effect. For these reasons, barium titanate is widely used in the electronic industry for manufacturing miniaturised multilayer ceramic capacitors, underwater transducers and self-regulating thermistors. BaZrxTi1-xO3 (BZT) solid solution possesses the perovskite structure and shows a series of phase transitions and a progressive evolution of ferroelectric order, from long-range order typical of classic ferroelectrics (x = 0-0.15), via a diffuse transition behaviour (x = 0.15-0.25), to short-range order typical of relaxors (x >= 0.25) and finally paraelectric non polar state for neat BaZrO3. The trivalent europium ion (Eu3+) is well known for its strong luminescence in the red spectral region. Even very small variations in the coordination sphere of europium ions induce major changes in the emission spectrum. Thanks to these features, Eu3+ is a unique and powerful local structural probe. In this framework, we have investigated the photoluminescence (PL) emission of dense BZT ceramics doped with Eu3+ at the Ba site with composition EuyBa1-yZrxTi1-x-y/4O3 (y = 0.01, x = 0, 0.05, 0.15, 0.30, 0.50, 0.70, 1) in the temperature range -100 to 140 °C. The ceramics were prepared by the classical solid-state route and sintered at 1450-1550 °C. The dielectric permittivity of the samples was measured from -150 to 150 °C at 10e2-10e6 Hz to determine reference values of the phase transition temperatures and the type of polar order. The PL bands revealed significant shape and intensity variations which can be correlated with the existence and nature (long-range or short-range) of polar order rather than the phase transitions. The spectral features observed for compositions with long-range ferroelectric order (x = 0-0.15) support the off-centre displacement of the Eu3+ ion with respect to the lattice position occupied by barium.

In this work was investigated the influence of processing conditions on PVDF polymorphism in PVDF/BaTiO3 composite dielectrics for energy storage applications

(1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BCTZ) pseudobinary ferroelectric (x is the molar percent of BCT) is one of the most promising BT-based materials for piezoelectric applications. In this work, a series of dense Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics with grain size larger than 1?m with uniform grain-size distribution were successfully prepared by the conventional solid-state reaction, and the grain-size effects on the structural, dielectric, ferroelectric and piezoelectric properties were explored in their un-poled and poled states. The ceramics were obtained by sintering solid state powders at different temperatures between 1400-1500°C and times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 2 ?m for the samples sintered at 1400 ºC/2h to 27 ?m for the samples obtained at 1500 ºC/24h. The evolution of polar order and phase transitions with grain size has been studied using dielectric permittivity measurements at 20Hz- 2MHz between 25 and 150 °C. The low and high field investigations (P(E) hysteresis loops and dc-tunability) showed that exist a critical grain size (~ 9 ?m) for which the properties are higher. In addition, we develop a mesoscale modelling (Monte Carlo with Finite Element Method calculations) to describe size effects on the low-field properties in BCTZ ceramics. The presented data provide a complete picture of the size effect dependence of functional properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics. Acknowledgment: The financial support of the PN III-P1-1.1-TE-2016-1951 is acknowledged.

The incorporation of homovalent M4+ ions at the Ti site of BaTiO3 with formation of the BaMxTi1-xO3 solid solutions (M = Sn, Zr, Hf, Ce) determines significant modifications of the phase transitions, polar order and functional properties. These materials are attractive for applications such as high energy density capacitors, tunable microwave dielectrics and electrocaloric effect-based cooling devices [1-3]. Unlike the systems containing Sn and Zr, the impact of structural disorder and local structure on the evolution of polar order and properties in Ce-doped barium titanate ceramics has not been investigated in detail yet. Dense (97-99% rel. density) ceramic samples with composition BaCexTi1-xO3 (x = 0.02, 0.05, 0.06, 0.10, 0.12, 0.15, 0.175, 0.20 and 0.30) were prepared by the conventional solid-state route starting from fine precursor powders and sintered at 1450-1500 °C. The average crystal structure at different temperatures in the range 100-400 K was determined from the Rietveld refinement of high-energy X-ray diffraction data collected at ESRF. The pair distribution function analysis was used to investigate the local structure and the level of disorder. The phase transitions and the evolution of polar order with composition were studied using dielectric permittivity measurements at 100 Hz-1 MHz between -150 and 150 °C, variable temperature Raman spectroscopy (from -195 to 165 °C) and differential scanning calorimetry (-100 - 150 °C). The ferroelectric hysteresis loops were measured at room temperature. Overall, the data provide a detailed picture of the BaCexTi1-xO3 system and a composition-temperature phase diagram will be proposed. A polar local structure exists irrespective of the long-range average symmetry for all compositions. Differently from the homologous systems BaSnxTi1-xO3 and BaZrxTi1-xO3, a diffuse ferro/para transition is already observed at x = 0.05 as a consequence of the high level of lattice disorder while relaxor behaviour occurs when x >= 0.20. References [1] V. V. Shvartsman, D. C. Lupascu, J. Am. Ceram. Soc., 95, 1-26 (2012) [2] X. S. Qian et al., Adv. Funct. Mater., 24, 1300-1305 (2014) [3] V. Buscaglia et al., J. Phys: Condens. Matter, 26, 065901 (2014)

One of the most promising BT-based materials for piezoelectric applications is the pseudobinary ferroelectric (1-x)Ba(Zr0.2Ti0.8)O3-x(Ba0.7Ca0.3)TiO3 (BCTZ) (x is the molar percent of BCT). In the present paper, we present preparation and functional characterisation of Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics with grain size larger than 1 ?m. The powders were prepared by the conventional solid-state route starting from fine precursor powders and calcined at 1000°C/4 hours. Dense ceramics (relative density above 94-98%) with different grain size were obtained by sintering the resulted powders at temperatures between 1400-1500°C for different times (from 0.2-24 hours). The grain size of ceramics determined from SEM images were between 2 ?m for the samples sintered at 1400C/2h to 27 ?m for the samples obtained at 1500°C/24h. The evolution of polar order and phase transitions with grain size has been studied using dielectric permittivity measurements at 1Hz- 1MHz between 25 and 150°C. The high field dielectric properties (dc-tunability) show a slight modification with grain size. The presented data provide a complete picture of the size effect dependence of functional properties in Ba0.85Ca0.15Ti0.90Zr0.10O3 ceramics. Acknowledgment: This paper was performed during ECOST-STSM-MP1308-191116-081333.

BaTiO3 nanoparticles (100÷150 nm), prepared in-house by a hydrothermal-like method starting from BaCl2 and TiCl4 precursors, were dispersed into a matrix of poly(vinylidene fluoride) (PVDF, Solef 6008 Solvay). 0-3 connectivity composites containing up to 35 vol% of ceramic inclusions were obtained either by solution casting or melt blending in a Brabender type batch-mixer; a compression moulding step was performed to obtain sheets 0.5-1 mm thick enriched in the electro-active ? polymorph of PVDF. Bare and surface-modified BaTiO3 particles were used, modification included functionalization with silane-based coupling molecules and/or coating with a thin shell of TiO2 (k ? 100). Such engineered polymer/ceramic interfaces should facilitate a fine dispersion of the inclusions by realizing, from the particle core to its surface, a gradient of the dielectric constant giving a more homogeneous distribution of the electric field in the resulting composites. Morphological and microstructural features of particles and composites were investigated by TEM and SEM-EDX microscopy, respectively. The amount of the ferroelectric crystalline ? phase in the PVDF matrix was determined by ATR-FTIR spectroscopy and X-ray diffraction. The dielectric constant and the loss tangent of the composites were measured at different frequencies by impedance spectroscopy. Simulations of electric field distribution performed by 3D finite element modelling were correlated with the experimental evidences.

The demand for high dielectric constant materials and high energy density capacitors has rapidly increased in recent years due to the continuous and rapid development of the electronic industry and the need to store electrostatic energy more efficiently. The combination of dissimilar materials in a composite represents an effective approach for the optimization of the dielectric properties. The addition of ferroelectric (barium titanate, BaTiO3) nanoparticles with high dielectric constant (k 1000) enables the relative dielectric constant of the polymer (k 3-10) to be significantly increased without compromising some of the most useful properties of the material. Polymer composites were prepared using polyvinylidene fluoride (PVDF) as a matrix and BaTiO3 nanoparticles (d~100 nm) as inclusions. The composites were fabricated by mixing PVDF and BaTiO3 particles at 200°C using the melt-blend method. The microstructure was observed on fracture surfaces by SEM. The amount of ferroelectric beta phase in the PVDF matrix was determined by FT-IR spectroscopy and the dielectric propeties were determinated at different frequencies and temperature by impedance spectroscopy. Simulation of the field distribution in model composites was performed by 3D finite element modelling.

BaTiO3-based ferroelectric ceramics show interesting properties such as high dielectric constant, low losses, high hydrostatic piezoelectric coefficient and PTCR effect. For these reasons, barium titanate is widely used in the electronic industry for manufacturing miniaturized multilayer ceramic capacitors, underwater transducers and self-regulating thermistors. BaZrxTi1-xO3 (BZT) solid solution shows a series of phase transitions and a progressive evolution of ferroelectric order, from long-range order typical of classic ferroelectrics (x = 0) to short-range order typical of relaxors (x >= 0.25), which consequently affects the functional properties. This material can be considered as a model system for understanding the composition-property correlations in ferroelectric ceramics. The trivalent europium ion (Eu3+) is well known for its strong luminescence in the red spectral region. Even very small variations in the coordination sphere of europium ions induce major changes in the emission spectrum. Thanks to these features, Eu3+ is a unique and powerful local structural probe. In this framework, we used photoluminescence (PL) as a tool to investigate the phase transitions and the ferroelectric order in BZT using Eu3+ as active centre. Dense ceramics (relative density: 96-99%) with composition EuyBa1-yZrxTi1-x-y/4O3 (y = 0.01, x = 0, 0.05, 0.15, 0.30, 0.50, 0.70, 1) were prepared by the classical solid-state route and sintered at 1450-1500 °C. The dielectric permittivity of the samples was measured from -150 to 150 °C and at 102-106 Hz to determine reference values of the phase transition temperatures. The study of PL spectra as a function of temperature, in the interval -100 to 140 °C, revealed strong shape and intensity variations of the emission bands in the proximity of phase transitions as well as a significant dependence of the band intensity on x in the composition region (x >= 0.30) corresponding to the relaxor behaviour.

BaTiO3 perovskite and its solid solutions, as BaTi1-xMIVxO3, are nowadays the most used ferroelectric. These materials are friend-environmental ferroelectrics, being lead-free, and show excellent properties. In this light, they are very useful in very different fields, but unfortunately their characteristics limit their applications in nano technology. Indeed, in these perovskites, the reduced size induces the so called "size effect" which consists in a disappearance of the ferroelectricity under a critical grain size [1]. This degradation of the material properties is then really problematic considering the present tendency in device miniaturization. In order to better understand this phenomenon, many studies have been performed. In pure BaTiO3 the "size effect" and the polarization reduction seem to be linked to the increasing local structural disordered nature of the nano powders as reported by Petkov et al. [2], Page et al. [3], Yoneda et al. [4]. However similar conclusions are not be previously proposed for doped BaTiO3, then the case of nano BaTi1-xCexO3 perovskite is here presented. The purpose is to explore the relation between the reduced size and the structure, as a function of cerium amount. Rietveld method and Pair Distribution Function were applied to give a complete picture of the average and local structure. Data collection was performed at ID22, European Synchrotron Radiation Facility (ESRF), Grenoble, France [5]. In this case study the use of the synchrotron radiation and an appropriate instrumentation is essential. In one hand high resolution data were necessary to recognize phase transitions, observable despite the peak broadness caused by the nano size of the material. On the other hand, in order to obtain suitable Pair Distribution Functions, data has to be collected at very high Qmax. The high quality of the data allowed to obtain good results on both average and local structure. Performed analyses show how the reduced size and the doping amount act at the structural level and how this is linked to the material properties. [1] N. Nuraje, K. Su, Nanoscale 2013, 5(19), 8752-8780. [2] V. Petkov, V. Buscaglia, M.T. Buscaglia, Z. Zhao, Y. Ren, Physical Review B 2008, 78(5). [3] K. Page, T. Proffen, M. Niederberger, R. Seshadri, Chemistry Of Materials 2010, 22(15), 4386-4391. [4] Y. Yoneda, S. Kohara, K. Kato, Japanese Journal Of Applied Physics 2013, 52(9, 2, SI). [5] www.esrf.eu

There is an increasing demand of high permittivity (high-k) materials due to the rapid development of the electronic industry and the need of more efficient energy storage devices. The combination of dissimilar components in composites is expected to be an effective approach to better dielectric materials. The inclusion of high-k particles, such as Ag and BaTiO3, in a polymeric matrix can significantly increase the dielectric constant while preserving the flexibility and the high breakdown voltage typical of polymers. The combination of high-permittivity and large breakdown fields is a fundamental requirement to store electrostatic energy with high density. Ferroelectric BaTiO3 nanoparticles (50-100 nm) were obtained by a hydrothermal-like method starting from cheap inorganic precursors (BaCl2 and TiCl4). The size of the particles was tailored by changing the precursor concentration. Silver particles (20-200 nm) were synthesized by a solvothermal method using ethylene glycol as a solvent and AgNO3 as a precursor and adding polyvinylpyrrolidone (PVP) as growth modifier to control the particle size. The nature of the inclusion-polymer interface has a strong impact on the dispersion of the inorganic particles and the dielectric properties of the resultant composite. The compatibility between the two phases was improved by functionalizing the particles with specific coupling molecules, such as silane-based compounds. As a further strategy to improve the dielectric properties of the composite, the particles were coated with a thin TiO2 shell, which has a dielectric constant intermediate between the filler and the polymer matrix and thus realizes a more homogeneous distribution of the electric field.

BaTiO3-based ferroelectric ceramics show interesting properties such as high dielectric constant, low losses, high hydrostatic piezoelectric coefficient and positive coefficient of resistivity. For these reasons, barium titanate is widely used in the electronic industry for manufacturing miniaturized multilayer ceramic capacitors, underwater transducers and self-regulating thermistors. BaZrxTi1-xO3 (BZT) solid solution shows a series of phase transitions (PT) and a progressive evolution of ferroelectric order, from long-range order typical of classic ferroelectrics (y = 0) to short-range order typical of relaxors (x >= 0.25), which consequently affects the functional properties. This material can be considered as a model system for understanding the composition-property correlations in ferroelectric ceramics. The trivalent europium ion (Eu3+) is well known for its strong luminescence in the red spectral region. Even very small variations in the coordination sphere of europium ions induce major changes in the emission spectrum. Thanks to these features, Eu3+ is a unique and powerful local structural probe. In this framework, we used photoluminescence (PL) as a tool to investigate phase transitions and the ferroelectric order in BZT using Eu3+ as active centre. Dense ceramics (relative density: 96-99%) with composition EuxBa1-xZryTi1-y-x/4O3 (x = 0.01, y = 0, 0.05, 0.15 and 0.30) were prepared by the classical solid-state route and sintered at 1450-1500 °C. The dielectric permittivity of the samples was measured from -150 to 150 °C and at 102-106 Hz to determine reference values of the phase transition temperatures. The study of PL spectra as function of the temperature, in the interval -100/140 °C, revealed strong shape variations in the PT proximity thus allowing the identification of the stability range of the different crystalline phases.

Dielectric responses of ceramics from the lead-free isovalent BaZrO3-BaTiO3 (BZT) system were investigated from Hz frequencies up to the infrared in a broad temperature range, 10-700 K. Pure BaZrO3 is a displacive weak-incipient ferroelectric with a simple cubic perovskite structure down to low temperatures, whose dielectric response is fully determined by polar phonons, the lowest-frequency one being of the Last type, unlike BaTiO3, where it is of the Slater type. BaZr0.4Ti0.6O3 is a relaxor ferroelectric whose dielectric anomaly is caused by a strong, overdamped excitation, which softens from the THz down to MHz range according to the Arrhenius law and merges into a constant-loss background at low temperatures. Such a reponse is similar to lead-containing and heterovalent relaxors, but unlike them, the lowest-frequency TO1 polar phonon does not soften appreciably. In the case of BaZr0.2Ti0.8O3 we have investigated the dynamic response connected with a diffuse ferroelectric phase transition. The main dielectric anomaly is again due to similar overdamped THz-microwave excitation, which, however, softens only to the GHz range near the transition temperature and below it merges with a near-constant-loss background. The picture of polar nanoregions in BZT differs from that in heterovalent relaxors, because they are pinned to the regions of the off-centered Ti4+ ions, which are frozen in our temperature range. Therefore we assign the soft relaxations to hopping of the off-centered Ti4+ ions. This is compared with the behavior of pure BaTiO3 ceramics, in which the hopping of the off-centered Ti4+ ions also substantially contributes to the phase transition dynamics. Unlike BaTiO3, the dynamic instability, which is responsible for the diffuse ferroelectric and relaxor behavior in BZT, is fully due to the hopping dynamics of the off-centered Ti4+ ions rather than due to soft phonons, and therefore the diffuse transition is of the order-disorder type

The interrelated semiconductor and ferroelectric properties of n-doped BaTiO3 ceramics were considered for describing their electrical properties in a large range of temperatures. A double barrier Schottky model (Heywang-Jonker) combined with the Landau-Devonshire model were used in order to explain the ferroelectric-semi conductor properties of n-doped BaTiO3 ceramics with PTCR characteristics. The resistivity-temperature R(T) dependencies were simulated for various model parameters, in the whole range of temperatures, including the fierro-para phase transition. A limited range of the donor concentration and of the surface state density for the semiconductive behaviour at room temperature was obtained from the model, similar as in experiments. The results obtained for different model parameters were discussed in connection with the composition and processing parameters of BaTiO3-based PTCR materials.