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Electronic and dielectric properties are essential for understanding many functional materials, predicting their behavior and optimizing their performance across different shapes, geometries and scales. Several approaches were developed and explored to investigate more or less deeply the appropriate properties. One of the most appealing, accurate and efficient approach is first principle simulations based on modern theory of polarization. Especially with the increased availability of powerful computational resources and techniques. Building upon these advancements, our contribution aims to elucidate an efficient methodology for studying electronic and dielectric properties by applying the Berry phase and Maximally Localized Wannier functions methods. Our exploration will initially focus on a systematic study of the electronic, chemical bonding, ferroelectric and piezoelectric properties of the well-known prototypical bulk system PbTiO3. Subsequently, we will extend our study to examine slab properties as surface termination and slab thickness effect on electronic properties, utilizing the robust Wannier-justified Tight Binding model. [ABSTRACT FROM AUTHOR]

Engineering new photoanode materials to substantially improve the efficiency of natural dye-sensitized solar cells (DSSC-Ns) is a significant challenge in the field of DSSC-Ns. This study utilizes the doctor blade technique to develop novel photoanode materials based on mixtures with different proportions of TiO2 Hombikat UV100 and TiO2 P25, two nanometric powders with different grain sizes. The fabricated films were studied by X-ray diffraction, which revealed a dominant anatase phase in the structure, as was corroborated by Raman spectroscopy. The crystallite size of the materials was determined using the Scherrer method. Using optical measurements, we estimated the bandgap energy (Eg) of the photoanodes that varied in the samples at around 3 eV. The assembled solar cells demonstrated a significant efficiency of 4.87% in the TiO2 Hombikat UV100/TiO2 P25 sample with the proportion of 50–50% (HP50) of blended photoanode. This sample device exhibited a fill factor of 50.41%, an open circuit voltage (Voc) of 0.65 V, and a current density of 14.75 mA/cm2 for an active surface area of 0.19 cm2. The HP50 sample constituted highly efficient DSSC-Ns and photoanodes with lower open-circuit voltage in the series, while HP40 developed a Voc of 0.73 V, and HP30 developed a Voc of 0.70 V. [ABSTRACT FROM AUTHOR]

This study reports the fabrication and characterization of Nd2Ru2O7 (NRO) pyrochlore-based dye-sensitized solar cell. This new photovoltaic cell uses a new stack material Glass/FTO/TiO2/Nd2Ru2O7/hibiscus/Pt/FTO/Glass. Nd2Ru2O7 pyrochlore oxide was elaborated as mesoporous nanoparticles dispersed in dimethylformamide (DMF) and deposited via spin coating onto the compact TiO2 compact layer previously deposited on FTO-coated glass substrate. Hibiscus sabdariffa was used as absorbent dye on the NRO photoanode. The optical properties of the films showed highly performance of absorbance ~ 70% and transmittance below ~ 50%. Dye-impregnated photoanodes have a high absorbance that covers the visible spectral range (360 nm–1000 nm). These assembled photoanode materials give an open-circuit voltage Voc of 2.86 V. The efficiency of the natural dye solar cell (DSSC-N) with the new NRO photoanode increased by a factor of 1.35 compared with the simple TiO2-based solar cell. The assembled cell, subsequent to the introduction of hibiscus dye and the I−/I3− electrolyte, yielded compelling outcomes: a Voc of 2.86 V, an efficiency of 10.24%, a short-circuit current density of 6.5 mA/cm2 in the dark, and 8.5 mA/cm2 under illumination. Importantly, all these findings are original, showcasing the effectiveness of our novel approach in enhancing the performance of dye-sensitized solar cells. [ABSTRACT FROM AUTHOR]

High-performance photovoltaic devices require active photoanodes with superior optoelectric properties. In this study, we synthesized neodymium ruthenate, Nd2Ru2O7 (NRO), and gadolinium ruthenate pyrochlore oxides, Gd2Ru2O7 (GRO), via the solid-state reaction technique, showcasing their potential as promising candidates for photoanode absorbers to enhance the efficiency of dye-sensitized solar cells. A structural analysis revealed predominantly cubic symmetry phases for both materials within the Fd-3m space group, along with residual orthorhombic symmetry phases (Nd3RuO7 and Gd3RuO7, respectively) refined in the Pnma space group. Raman spectroscopy further confirmed these phases, identifying distinct active modes of vibration in the predominant pyrochlore oxides. Additionally, a scanning electron microscopy (SEM) analysis coupled with energy-dispersive X-ray spectroscopy (EDX) elucidated the morphology and chemical composition of the compounds. The average grain size was determined to be approximately 0.5 µm for GRO and 1 µm for NRO. Electrical characterization via I-V measurements revealed that these pyrochlore oxides exhibit n-type semiconductor behavior, with conductivity estimated at 1.5 (Ohm·cm)−1 for GRO and 4.5 (Ohm·cm)−1 for NRO. Collectively, these findings position these metallic oxides as promising absorber materials for solar panels. [ABSTRACT FROM AUTHOR]

Multiferroic materials with coexisting of at least two ferroic orders (ferromagnetic, ferroelectric, or ferroelastic) have recently attracted the interest of researchers due to their potential applications as multifunctional devices. Herein, we report the synthesis and detailed characterization of the multiferroic CoFe2O4–Ba0.95Ca0.05Ti0.89Sn0.11O3 core–shell nanofibers (CFO@BCTSn NFs) prepared by a sol–gel coaxial electrospinning technique. The scanning and transmission electron microscopes were used to check nanofibers' core–shell structure/configuration, with fiber diameters ranging from 150 to 250 nm. The X-ray diffraction analysis confirms the presence of both the spinel structure of the CFO and the perovskite structure of the BCTSn. Piezoresponse force microscopy and magnetic hysteresis were used to confirm the multiferroicity of CFO@BCTSn NFs. Notably, the maximum magnetization and remanent magnetization of NFs are found to be 11.63 emu g–1 and 1.43 emu g–1, respectively. Meanwhile, the maximum piezoelectric response d33eff is around 6 pm V–1. The magnetoelectric (ME) coefficient obtained for the CFO@BCTSn NFs is 346 mV cm–1 Oe–1 at the field of 10 kG. These findings may lead to development of nanoscale Pb-free magnetic field sensors and magnetoelectric device applications. [ABSTRACT FROM AUTHOR]

New multiferroic particulate composites (1-x) Ba0.95Ca0.05Ti0.89Sn0.11O3–(x) CoFe2O4 with (x = 0.1, 0.2, 0.3, 0.4 and 0.5) have been prepared by mechanical mixing of the calcined and milled individual ferroic phases. X-ray diffraction and Raman spectroscopy analysis confirmed the formation of both perovskite Ba0.95Ca0.05Ti0.89Sn0.11O3 (BCTSn) and spinel CoFe2O4 (CFO) phases without the presence of additional phases. The morphological properties of the composites were provided by using field emission scanning electron microscopy. The BCTSn-CFO composites exhibit multiferroic behavior at room temperature, as evidenced by ferroelectric and ferromagnetic hysteresis loops. For all composites, the converse piezoelectric coefficient was calculated and found to decrease from 203 pm.V−1 to 27 pm.V−1 in pure BCTSn. when the CFO content increases. The magnetoelectric (ME) coupling was measured under a magnetic field up to 10 kOe and the maximum ME response found to be 0.1 mV.cm−1.Oe−1 for the composition 0.7 BCTSn-0.3 CFO exhibiting a high degree of pseudo-cubicity and large density. [ABSTRACT FROM AUTHOR]

Ferroelectric property that induces electrocaloric effect was investigated in Ba(GexTi1−x)O3 ceramics, known as BTGx. X-ray diffraction analysis shows pure perovskite phases in tetragonal symmetry compatible with the P4mm (No. 99) space group. Dielectric permittivity exhibits first-order ferroelectric-paraelectric phase transition, confirmed by specific heat measurements, similar to that observed in BaTiO3 (BTO) crystal. Curie temperature varies weakly as a function of Ge-content. Using the direct and indirect method, we confirmed that the adiabatic temperature change ΔT reached its higher value of 0.9 K under 8 kV/cm for the composition BTG6, corresponding to an electrocaloric responsivity ΔT/ΔE of 1.13 × 10−6 K.m/V. Such electrocaloric responsivity significantly exceeds those obtained so far in other barium titanate-based lead-free electrocaloric ceramic materials. Energy storage investigations show promising results: stored energy density of ~17 mJ/cm3 and an energy efficiency of ~88% in the composition BTG5. These results classify the studied materials as candidates for cooling devices and energy storage applications. [ABSTRACT FROM AUTHOR]

Structural, dielectric, ferroelectric, energy storage properties, and electrocaloric effect were studied in lead-free ceramic Ba0.95Ca0.05Ti0.89Sn0.11O3 (BCTSn) elaborated by the sol–gel method. Phase purity structure was confirmed from X-ray data using the Rietveld refinement analysis which revealed the coexistence of tetragonal (P4mm) and orthorhombic (Amm2) symmetries at room temperature. Phase transitions were detected by dielectric and differential scanning calorimetry measurements. The energy storage properties were determined from P-E hysteresis, and the electrocaloric properties were calculated indirectly via the Maxwell approach. The large value of electrocaloric temperature change of ΔT = 0.807 K obtained at a relatively small electric field of 30 kV cm−1, and the high energy storage efficiency can make BCTSn ceramic a promising candidate for environmentally friendly refrigeration and energy storage applications. [ABSTRACT FROM AUTHOR]

The effects of 2% Zr introduction in Ba0.8Ca0.2TiO3 (BCT) system on its electrical and electrocaloric properties was investigated. BCT and Ba0.8Ca0.2Zr0.02Ti0.98O3 (BCZT) ceramics synthesized by solid-state processing were crystallized in a pure perovskite phase with a group space P4mm. After Zr insertion, the enhanced dielectric constant was obtained around the Curie temperature (Tc) in BCZT ceramic (εr = 6330 at Tc = 388 K) compared to BCT ceramic (εr = 5080 at Tc = 388.6 K). Moreover, the large-signal piezoelectric coefficient (d 33 ∗) was improved from 270 to 310 pm/V in BCT and BCZT ceramics, respectively, under a moderate electric field of 25 kV/cm. The electrocaloric effect was determined via indirect and direct methods. In the indirect approach, the electrocaloric temperature change (ΔT) was calculated via Maxwell relation, and the measured ferroelectric polarization P (E, T) extracted from the P–E curves recorded at 24 kV/cm. The maximum values of ΔT = 0.68 K and the electrocaloric responsivity ζ = 0.283 K mm/kV obtained at 385 K in BCZT ceramic were found to be higher than those observed in BCT ceramic (ΔT = 0.37 K and ζ = 0.154 K mm/kV at 387 K). In the direct approach, ΔT was measured utilizing a modified high-resolution calorimeter at 14 kV/cm. As the direct method is more sensitive to the latent heat, it provided larger values for smaller applied field, i.e., ΔT = 0.474 and 0.668 K for BCT and BCZT ceramics, respectively. A significant ζ of 0.477 K mm/kV was obtained in BCZT at 385 K and 14 kV/cm that matches the values found in lead-based materials. These results suggest that BCZT lead-free ceramics could have an excellent potential to be used in solid-state refrigeration applications. [ABSTRACT FROM AUTHOR]

Lead-free Ba0.85Ca0.15Zr0.10Ti0.90O3 (BCZT) ceramic exhibits excellent dielectric, ferroelectric and piezoelectric properties at the morphotropic phase boundary (MPB). Previously, we demonstrated that the use of the anionic surfactant sodium dodecyl sulfate (SDS, NaC12H25SO4) could enhance the dielectric properties of BCZT ceramic using surfactant-assisted solvothermal processing [1]. In the present study, structural, dielectric, ferroelectric properties, as well as electrocaloric effect and energy storage performances of this BCZT ceramic were thoroughly investigated. X-ray diffraction (XRD) measurements revealed the presence of single perovskite phase at room temperature with the coexistence of orthorhombic and tetragonal symmetries. In-situ Raman spectroscopy results confirmed the existence of all phase transitions from rhombohedral through orthorhombic and tetragonal to cubic symmetries when the temperature varies as reported in undoped-BaTiO3. Evolution of energy storage performances with temperature have been investigated. BCZT ceramic exhibits a high energy storage efficiency of ~ 80% at 120 °C. In addition, the electrocaloric responsivity was found to be 0.164 × 10−6 K·m/V at 363 K. [ABSTRACT FROM AUTHOR]