Diffuse Phase Transition Research Articles

Orthorhombic-tetragonal phase coexistence and enhanced piezoelectric properties at room temperature in Zn and Ta modified (Ba0.95Ca0.05)(Zr0.05Ti0.95)O3 ceramics through the synergistic effect of lattice distortion.

This study provides a fundamental understanding of the enhanced piezoelectric properties in ABO3 perovskite based lead-free piezoelectric materials. For this we synthesized (Ba0.95Ca0.05)(Zr0.05Ti0.95-x (Zn1/3Ta2/3) x )O3((1 - x)BCZT-(x)ZT) (x = 0.00, 0.005, 0.01, and 0.02) solid solutions exhibiting high piezoelectric response. The (1 - x)BCZT-xZT materials are synthesized by a high-temperature solid-state ceramic reaction method by varying x in the full range (x = 0.00-0.02). In-depth exploratory research is performed on the structural, dielectric, ferroelectric, and piezoelectric properties of (1 - x)BCZT-(x)ZT ceramics. The formation of perovskite structure for all ceramics without the presence of any impurity phases is confirmed by X-ray diffraction (XRD) analyses, which also reveals that the Ca2+, Zr4+, Zr2+ and Ta5+ are well dispersed within the BaTiO3 lattice. For all (1 - x)BCZT-(x)ZT ceramics, thorough investigation of phase formation and phase-stability using XRD, Rietveld refinement, Raman spectroscopy, and temperature-dependent dielectric measurements provide conclusive evidence for the coexistence of orthorhombic + tetragonal (Amm2 + P4mm) phases at room temperature. The steady transition of Amm2 crystal symmetry to P4mm crystal symmetry with increasing x content is also demonstrated by Rietveld refinement data and related analyses. The c/a ratio of the tetragonal phase greatly influenced the electric properties of the ceramics. The c/a ratio of the tetragonal phase increases from 1.0112 for x = 0 to 1.0157 for x = 0.005 and subsequently decreases to 1.0038 for x = 0.02. When the c/a of the tetragonal phase reaches its maximum value, the ceramic with x = 0.005 has the best piezoelectricity (d 33 ∼ 297 pC N-1). The calculated degree of relaxation (γ) increases with the increase in BZT content, indicating that the BCZT-xBZT ceramics are ferroelectric materials with diffuse phase transition. Main dielectric, piezoelectric and ferroelectric parameters of (1-x)BCZT-xZT ceramics were optimized around x = 0.005 with a high piezoelectric coefficient (d 33 = 297 pC N-1), a remnant polarization (P r = 7.58 μC cm-2), spontaneous polarization (P s = 10.25 μC cm-2) and a high dielectric constant (ε max,T c = 4449 at T c and 2330 near RT) at 1 kHz, indicating promising applications for lead-free piezoelectric ceramics.

Effects of La doping on diffused ferroelectric phase transition, electric and dielectric properties of lead-free SrBi2Ta2O9 ceramics

Citric acid-assisted method was used to synthesize pure polycrystalline La-doped SrBi2Ta2O9 powders which were uniaxially pressed and sintered under different conditions. La doping of SrBi2Ta2O9 resulted in the shortening of Ta-O bond lengths, but increased the unit cell volume and decreased the crystallite size. The effect of sintering process on dielectric properties was studied in order to find optimal sintering conditions. Dielectric loss, measured at room temperature, increases when sintering temperature rises from 1100 to 1200?C, as well as when sintering time increases from 6 to 9 h. Thus, further investigation was performed on the sample sintered at 1100?C for 6 h. The obvious change in ?? around TC and diffusive phase transition, pronounced for the ceramics with higher La content, were characteristic of the doped ceramics. The diffused ferroelectric phase transition behaviour is caused by structural disorder at the Sr-sites (Sr, Bi and La cations) in the Bi2O2 layers and perovskite blocks. The electrical conductivity increases steadily at lower temperatures (below 200 ?C), but shows a strong temperature- and frequency-dependent trend at higher frequencies. La-doping decreases conductivity by hindering charge carriers? long-distance mobility.

Effect of Laser Irradiation and Tensile Stress on Microstructure and Magnetic Properties of Fe-Based Amorphous Alloys.

The effect of laser irradiation and tensile stress on the microstructure and soft magnetic properties of the FeSiBNbCu nanocrystalline alloy prepared using a continuous laser has been investigated. The experimental results indicate that a decreased laser scanning speed provides more thermal energy to induce nanocrystals and encourage grain growth. When the scanning speed is excessively high, the crystallization process will cease due to a lack of energy to drive diffusion phase transitions. Nevertheless, the introduction of tensile stress could significantly promote crystallization in FeSiBNbCu alloy samples irradiated at these high laser scanning speeds. This phenomenon can be attributed to the augmentation of compressive thermal stress at the interface between the laser-treated track and the untreated region. This heightened compressive stress promotes the diffusivity of atoms, and, as a result, the transformation from amorphous to crystalline states can be enhanced. As the applied tensile stress increases, both grain size and crystalline volume fraction exhibit a proportional augmentation. Consequently, these changes manifest in the soft magnetic properties. The crystalline volume fraction can reach 62%, and the coercivity is 2.9 A/m at the optimized scanning speed; these values correspond to 54% and 3.3 A/m under specific tensile stress loading.

Experimental study of phase transition heat of composite thermal energy storage materials paraffin wax/expanded graphite

In this paper, the effect of the expanded graphite (EG) matrix on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the paraffin wax (PW) containing EG (up to 6.5 wt%) was explored in terms of the effective heat capacity and a diffuse phase transitions enthalpy difference over the 25–65 °С temperature range. Composite PCMs PW/EG was prepared using a new method and were inherent in high pores fill factor. The main advantage of the proposed method is preliminary vacuuming of the PW and EG with subsequent mixing and sonication under vacuum. The EG choice was based on the hypothesis that the EG matrix contributes to modifying the PW internal structure due to the PW molecules' adsorption on the EG surface during PCM cooling and solidification. Consequently, a significant change in PW/EG caloric properties vs. pure PW was observed. The EG presence in PW reverses the enthalpy hysteresis in the heating-cooling cycle vs. pure PW. The enthalpy difference during PW heating and melting in the range of 30–60 °С is higher than during its cooling and solidification: 336.2 J∙g−1 vs. 214.9 J∙g−1. On the contrary, the enthalpy difference of melting for PW/EG of 3.6 wt% in the range 30–60 °С was 171.2 J∙g−1 vs. 273.8 J∙g−1 during solidification. The obtained results are explained by the different dynamics of processes of PW melting and solidification in EG matrix pores. The presence of the 3.2–6.5 wt% of EG in PW contributes to an increase in solidification enthalpy difference in the range 30–60 °C on 27–33 % vs. pure PW. A decrease in the melting enthalpy difference for PW/EG on 44–50 % vs. pure PW was recorded in the range of 30–60 °C. In addition, thermal conductivity was measured to confirm the advantages of PW/EG as PCM. Thermal conductivity for PW/EG with EG content of 3.6 and 6.5 wt% at 25 °C was 8.9 and 9.6 times higher than for pure PW. Similarly, 8.8 and 10.9 times thermal conductivity increase was observed at 65 °C. The composite PCM containing 3.6 wt% of EG in PW obtained by developed method can be recommended as a rational composition in benefit of the thermal conductivity and caloric properties for utilization in high-performance TES systems.

Tailoring frequency/temperature independent colossal dielectric constant in Zn-doped Fe3O4/Fe2O3@C/PANI using phase co-existence approach

Introducing doped binary oxides to polymers offers a promising way towards advancement of charge density/energy storage materials with colossal dielectric constant. However, the origin of colossal dielectric constant explored in terms of conduction mechanism with a deeper understanding of the coexistence of phases/interfaces in these materials still requires much attention. In this context, we synthesised Zn-doped Fe3O4/Fe2O3@C/PANI composite that exhibits frequency and temperature independent colossal dielectric constant over a broad range, 1 Hz to 10 MHz and 93 K to 333 K, respectively. We analyzed the impedance data using an equivalent circuit model and Cole-Cole fitting to gain insight into the colossal dielectric response and low dielectric loss. The relaxation phenomenon corresponding to a highly stable electroactive region is validated by the distribution of relaxation time (DRT). Furthermore, the composite exhibited a non-relaxor-like behavior due to diffuse phase transition near semiconductor-to-metallic transition (SMT), observed at 303 K. The charge carriers follow the variable range hopping (VRH) and Arrhenius models yielding localization length of 3 Å and activation energy of 35 meV, which supports the charge transport mechanism between like cation interfaces. This detailed analysis covering the frequency and temperature independent dielectric constant along with the understanding of relaxation and conduction phenomena could provide a viable approach towards producing charge density/energy storage devices for practical applications.

High dielectric temperature stability in the relaxor ferroelectric thin films via using a multilayer heterostructure

The temperature stability of the relaxor ferroelectrics (RFEs) mainly originates from the diffuse phase transition (DPT). Higher atomic disorder degrees, more inhomogeneous lattice distortion and polymorphic phases could increase the compositional inhomogeneity for a stronger DPT. This work aims to enhance this compositional inhomogeneity for a high dielectric temperature stability by preparing the multicomponent RFE-based multilayer heterostructure polycrystalline thin films. The as-prepared RFE thin films show a relatively high dielectric constant (∼165.14), and a very high dielectric temperature stability with a very low relative variation ratio of dielectric constant (∼1.7 %) from -55 °C to 150 °C which can be comparable to most linear dielectric thin films. Meanwhile, the dielectric loss and leakage current densities were also optimized. This work brings the potential application of the RFE thin films in the thin-film capacitor with high temperature stability requirements.

Structure, dielectric and ferroelectric Properties of (1-x)K0.5Na0.5NbO3 – xBi0.5Na0.5TiO3(0 ≤ x≤ 0.1) Solid Solution

In this study, we prepared lead-free (1-x)K0.5Na0.5NbO3 – xBi0.5Na0.5TiO3 ceramics (KNNBTx) with x = 0, 0.025, 0.05, 0.075, 0.1 using the conventional solid-state reaction method. Scanning electron microscopy analysis revealed dense ceramics with a notable decrease of the average grain size from 3 μm for x = 0–0.3 μm for x ≥ 0.050. X-ray diffraction pattern refinement unveiled that the pure KNN possessed an orthorhombic Amm2 symmetry. In contrast, the KNNBT0.100 composition displayed a tetragonal P4mm symmetry, while the KNNBT0.025 composition exhibited a monoclinic Pm symmetry, suggesting the stabilization of an intermediate phase between the orthorhombic and tetragonal symmetries for x = 0.025. Dielectric measurements indicated that the introduction of small cations in A and B sites of the KNN matrix induced a diffusive phase transition. According to the modified Curie–Weiss law (named also Uchino and Nomura function), the degree of diffuseness (γ) increased from γ = 1.45 to γ 1.74 with increasing x. Raman spectroscopy revealed a frequency upshift of the vibration modes along with broadening of the modes as the NBT composition increased, indicating increased structural disorder in the perovskite structure. Temperature-dependent Raman spectra exhibited the persistence of certain modes at higher temperatures due to the off-centering of cations at A and B sites, a result of the induced substitution-induced disorder in the KNN matrix. Temperature dependent of Raman modes’ frequency have shown substantial modifications at temperatures close to the critical temperatures identified by dielectric measurements. Ferroelectric measurements demonstrated that the incorporation of NBT into the KNN matrix led to significant alterations in the polarization and ferroelectric characteristics of the parent ceramic (pure KNN). As the NBT content increased, the remanent polarization decreased from 13.1 to 3.6 μC/cm2, and the P-E curves became pinched/distorted, indicating a disruption in the long-range order of KNN due to structural and grain size modifications.

High-entropy (Na0.2Bi0.2Ba0.2Sr0.2Zn0.2)TiO3 ceramics with enhanced energy storage density and reliable stability

High-entropy ceramics (HECs) have gained increasingly recent interest due to their fantastic physiochemical properties and rich compositions. The investigation of energy storage performance based on the temperature and frequency stability of HECs is still at an early stage, with limited reported studies. Here, we report lead-free (Na0.2Bi0.2Ba0.2Sr0.2Zn0.2)TiO3 (NBBSZT) HECs by a solid-state approach with a pressureless sintering process. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies demonstrate that NBBSZT HECs show a pure perovskite structure, uniform morphology and element distribution. Ferroelectric measurements indicate that the NBBSZT HECs exhibit an improved energy storage density of 1.03 J/cm3 and an efficiency of 77%, which is approximately 5 times and 17 times enhancement compared to Bi0.5Na0.5TiO3 (BNT) ceramics, respectively. The NBBSZT HECs also demonstrate excellent thermal stability and satisfactory frequency stability. More interestingly, the dielectric property studies show that the NBBSZT HECs exhibit frequency dispersion and diffuse phase transition. Temperature-dependent dielectric measurements indicate that the NBBSZT HECs exhibit better relaxor characteristics than that of BNT ceramics. These studies reveal that the high-entropy strategy provides a potential platform for designing ferroelectric ceramics.

BZT substitution effect on the characteristics of (1-x) MT – x BZT composite ceramics synthesized by the sol–gel method

This paper addresses a crucial gap in the effect of adding BaZr0.1Ti0.9O3 (BZT) on the structural, microstructural, dielectric, and electrical properties of MgTiO3 (MT) material. These ceramics with the chemical composition (1-x) MT – x BZT were synthesized with different compositions ranging from × = 0.0 to 1.0 with a 0.1 step using the sol–gel reaction process. The X-ray diffraction (XRD) results and Rietveld refinement analysis showed the formation of a tetragonal phase with the P4mm space group for the BZT sample and a hexagonal phase with the R-3 space group for MT ceramics, without any secondary phases. However, (1-x) MT – x BZT composites with × ranging from × = 0.1 to 0.9, showed a coexistence of tetragonal (P4mm) and hexagonal (R-3) phases. Scanning Electron Microscopy (SEM) was used to investigate the morphology and grain size of the compounds. The SEM results revealed a clear decrease in grain growth for x = 0.6 of BZT content with the higher density. Furthermore, the dielectric properties of these composites were studied by impedance spectroscopy, which showed a single diffuse dielectric phase transition for all the BZT-MT composites. There was a clear increase in dielectric permittivity (εr′) value with the increase of the BZT content. This broad phase transition is highly desired and has not been observed in previous studies. The obtained composite ceramics could open the way to lead new applications in microelectronic devices.

A non-linear diffusion of amorphous Pt studied using a variable-order fractional model

A predictive understanding of the phase transition process from amorphous to crystalline in as-deposited films is critical for electronics and optoelectronic device applications. However, anomalous diffusion is frequently observed during the phase transition, making the prediction of device properties challenging. In this study, the diffusion procedure of amorphous Pt models, which was accompanied by the crystallization process, was investigated using a variable-order fractional (VOF) model. The competition between atom rearrangement and migration resulted in a non-linear diffusion. The diffusion procedure was divided into three stages based on variable-order exponent β(t) from the VOF model: amorphous-keeping, rapid-conversion, and slow-conversion; the diffusion coefficient K demonstrated the effects of temperature, component, and substrate on the diffusion properties. The VOF model captured features of the time-dependent diffusion of phase transition with a few parameters, allowing the quantitative comparison among distinct diffusion modes, and inspired the analysis of the complex non-linear diffusion procedure.

Effect of Ce infusion on the structural, dielectric, optical, transport and polarization behavior of Nd-modified triple-layered Aurivillius phase ceramic Bi3NdTi3O12

Herein, the effect of cerium substitution on the structural, dielectric, optical, impedance and leakage current characteristics of Nd modified triple layered Aurivillius phase compound of chemical composition Bi3NdTi3-xCexO12 is investigated. The polycrystalline samples are synthesized via ceramic fabrication technology. Room temperature X-ray analysis confirms their orthorhombic symmetry. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis affirm microstructure and elemental composition of the compounds. The temperature-dependent dielectric study indicates diffused phase transition (DPT) behavior possibly induced by compositional fluctuations and random occupancy of equivalent crystallographic sites. Signature peaks pertaining to metal-oxide bond vibrations are also identified by FTIR study. Impedance spectroscopic study unravels negative temperature coefficient of resistance (NTCR) and non-Debye type relaxation in the samples. UV–Visible spectroscopy reveals a reduction in band-gap from 3.1 eV to 2.83 eV with cerium infusion from x = 0 to x = 0.3. It is due to the introduction of localized mid-gap states thus, suggesting the possibility of photovoltaic applications. Further analysis of electric modulus and impedance characteristics propounds prominent short-range carrier hopping with higher cerium percentage. The room temperature I–V study suggests an increase in the voltage-dependent non-linearity with cerium incorporation. Leakage current analysis reveals a transition from Ohmic to space charge limited conduction (SCLC) type behavior with high electric field. Room temperature polarization study confirms their ferroelectric property. Frequency dependent ac conductivity obeys Jonscher double power law clearly indicating the presence of two dispersive regions dominated by grain and grain boundary effects. Reduced bandgap, enhanced voltage dependent non-linearity, NTCR type property and saturated P-E loops observed in the sample unravel the multifunctional aspects of the fabricated compound.

Boosting ultra-wide temperature dielectric stability of multilayer ceramic capacitor through tailoring the combination types of polar nanoregions

With the rapid development of space exploration and new energy vehicles, it is urgent to build ultra-wide temperature multilayer ceramic capacitors (UWT MLCCs) to match electronic circuits that can withstand harsh environmental conditions. Relaxor ferroelectrics with diffuse phase transition feature are potential dielectrics for the construction of UWT MLCCs. However, how to ensure high dielectric constant together with low dielectric loss in the wide temperature region is still a big challenge. Here, the above difficulties are addressed by tailoring the combination types of polar nanoregions (PNRs) in the (1-x) (0.8Na0.5Bi0.5TiO3-0.2K0.5Bi0.5TiO3)-xNaTaO3 (NBT-KBT-xNT) system. Compared with PNRs types of P4bm + R3c and P4bm + Pbnm, the combination type of P4bm + Pbnm + R3c PNRs in NBT-KBT-0.31NT is the most beneficial to obtain comprehensive excellent dielectric performance because it can balance the relationship between high dielectric constant and temperature stability over a wide temperature region. Further, by optimizing the laminating pressure and co-firing temperature to realize a tight interfacial structure between the dielectric layer and the Pt inner electrode, a record-high dielectric constant (εr = (907% ± 15%)) together with low dielectric loss (tanδ ≤ 0.025) is achieved over an ultra-wide range from −61 °C to 306 °C for NBT-KBT-0.31NT MLCC, demonstrating that tailoring the combination types of PNRs is a powerful strategy in designing UWT MLCC dielectrics.

Structure, Microstructure, and Dielectric Properties of Bi<sub>0.5</sub>(Na<sub>0.78</sub>K<sub>0.22</sub>)<sub>0.5</sub>TiO<sub>3 </sub>Lead-Free Ceramic

In this article, the structural, microstructural, and dielectric properties of Lead- free perovskite ceramic Bi0.5(Na0.78K0.22)0.5TiO3 [BNKT] have been reported. The material was synthesized through the solid-state reaction method. The compound formed is found to have a hexagonal structure, confirmed by XRD analysis of the sample. The microstructural analysis of the compound revealed the polycrystalline nature of the ceramic having quasi-cubic grain morphology with distinct grain boundaries. From the dielectric study, it was found that the dielectric constant increases with temperature and attained maximum value at temperature Tc = 335° C, after which it decreased. The frequency independence of transition temperature (Tc) suggested the classic ferroelectric behaviour of the compound. The broad dielectric peak around transition temperature confirms the relaxor behaviour of the compound as well as diffused phase transition at Tc. The value of the relative permittivity and loss tangent at ambient temperature for 1kHz frequency is 627 and 0.223 respectively. The synthesized material can be utilized for the fabrication of capacitors and energy storage applications.

Effect of Milling on Dielectric Properties of PZT

In this study, we investigated the impact of high-energy milling on the structural and dielectric properties of Pb[Zr(1-x)Tix ]O3 [PZT] ceramics synthesized using the solid-state reaction process. The sample was milled for 2, 4 & 6 hours using a high-energy ball milling machine. The unit cell structure for all of the samples was observed to be monoclinic, according to x-ray diffraction measurements (space group: C1m1). A significant reduction in crystallite size was observed, from 132 nm to 46 nm after 6 hours of milling. The dielectric study indicated a classical ferroelectric type behaviour for the un-milled sample and diffused phase transition for all milled samples. However dielectric constant dropped from 940 to 487 after 6 hours of milling.

The unexpected diffuse phase transition in relaxor-PbTiO3 ferroelectrics via acceptor modification

The diffuse phase transition (DPT) and domain structure are essential to the functional properties of relaxor ferroelectrics and are extremely sensitive to the ion doping. The utilization of acceptor doping has been observed to be an effective method in enhancing the high-power properties of relaxor ferroelectric materials. The present study aims to examine the acceptor-doped DPT and domain structure in single crystals of Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3. An unexpected physical phenomenon was identified in which Mn-doping increased dielectric diffusion and lowered domain size while suppressing dielectric relaxation. Traceability investigations suggest that Mn-doping inhibited the growth of polar nanoregions by enhancing random electric fields, which increases dielectric diffusion while decreasing the domain size. Meanwhile, Mn doping redistributes the relaxation time function, which results in a reduction in dielectric relaxation. The current research deepens the understanding of the physical basis of DPT and can be applied to the development of high-performance piezoelectric materials.

Evolution behavior of electrocaloric effect in BaTiO3‐based ceramics with different phase structures and phase transitions

AbstractIn this work, the evolution behavior of electrocaloric effect in BaTiO3‐based ceramics with different phase structures and phase transitions was compared. A paradigmatic system of (Ba0.85Ca0.15)(Ti1−xHfx)O3 ceramics was selected. Diffuseness exponent γ increases linearly with rising x. Electrocaloric temperature change (ΔT) shows an opposite variation, whereas temperature span (Tspan) displays the same tendency with γ changing. The degeneration of maximum polarization and polarization change rate contributes to the decrease in ΔT due to the diffusion phase transition, whereas the diffusion can lead to a large Tspan. The ceramic with a single ferroelectric or paraelectric phase shows a small ΔT but a high variation rate with elevating electric field (E), whereas a small variation rate is present in the phase‐transition region that shows a high ΔT. Besides, small electrocaloric strength (ΔT/ΔE) is obtained in the single‐phase region and increases with elevating E. A high ΔT/ΔE is present in the phase‐transition region but decreases with elevating E. When phase transition becomes diffusion, ΔT variation with E becomes obvious, whereas ΔT/ΔE dependence will decrease. These phenomena result from the difficult polarization orientation in single ferroelectric phase or weak polarization in paraelectric phase, and the easy polarization orientation in the phase‐transition region.

Structural Refinement, Dielectric and Electromechanical Properties of (1-x)NBT-xKBT Piezoceramics in the Morphotropic Phase Boundary Region

Lead-free ferroelectric materials of sodium-potassium bismuth titanate, (1-x)NBT-xKBT systems were synthesized by a hydrothermal process. In this way, the appropriate conditions for the hydrothermal synthesis of NBT and KBT (i.e., concentrations of synthetic precursors, solution pH and temperature) are given graphically. Ceramics of (1-x)NBT-xKBT with (x(mol.%) = 0; 12; 16; 20; 30 and 100) were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The rhombohedral-tetragonal morphotropic phase boundary (MPB) was confirmed to be in the region of 0.12 ≤ x ≤ 0.20 for (1-x)NBT-xKBT at ambient temperature. Scherrer's formula and the Williamson-Hall (W-H) analysis were used to examine the average crystallite size and lattice strain. Raman spectroscopy was effectively applied to study the structural evolution of the (1-x)NBT-xKBT phase. The ceramics exhibited a high temperature of maximum dielectric permittivity at (Tmax = 343 °C at 100 kHz) along with electromechanical coupling factors (kp = 0.34, d33 = 147 pC/N). Based on the composition of all specimens, the results indicate a diffuse phase transition, probably of second order, between ferroelectric and paraelectric phases.

Effect of fullerene C60 on phase transition enthalpy of paraffin wax: Calorimetry and structural analysis

In this paper, the effect of minor fullerene С60 admixtures on the phase transitions enthalpy of phase change material (PCM) is studied experimentally. For this purpose, the stable molecular solutions of the paraffin wax (PW) and fullerene С60 were explored in terms of the effective heat capacity and enthalpy of diffuse phase transitions over the (27…65) °С temperature range and C60 mass fraction up to 0.000746 g∙g−1. The choice of C60 as PW admixture was based on the hypothesis that a small amount of C60 contributes to a modification of the PW internal structure and, as a consequence, to a change in its caloric properties. Some factors that may affect the uncertainty for the obtained experimental data were examined. It was shown that the phase transition enthalpy for the PW/C60 in the (40…60) °C temperature range increase from 154.0 J∙g−1 (for pure PW) to 194.7 J∙g−1 (for PW containing 0.000746 g∙g−1 of C60) during cooling and decrease from 233.2 J∙g−1 (pure PW) to 182.3 J∙g−1 (PW containing 0.000746 g∙g−1 of C60) during heating. The results obtained indicate the defining influence of С60 on the PW structure in the liquid and solid states. It was confirmed by an additional structural analysis, which reported that pure PW has a minimal cell volume compared to PW/С60. The C60 addition into PW contributes to the expansion of the cell, indicating that the molecules lose their tight packing. A clear dependence between the enthalpy of melting and unit cell volume for PW/C60 samples was found. It was observed that unit cell expansion of PW due to the addition of C60 reduces the enthalpy hysteresis in the heating-cooling cycle – a key parameter that affects the efficiency of a thermal energy storage material. This positive effect may be due to structural transformation in PW during the melting-solidification cycles.

Dipole engineering: Properties of In3+ and Ta5+ dipole substituted BaTiO3

Dopants play a significant role in electronic material design. In semiconductors, donor and acceptor doping enhance electron and hole conduction, respectively, while simultaneously donor and acceptor doping counteract one another. The role of dopants versus substitutions within dielectrics are not as well studied nor are the effects as well understood. From semi-conductor theory dopant is addition of a small fraction of atoms, roughly less than one part in ten-thousand (to parts per million), and it is not a charge neutral process. In this investigation, the effects of dipole substitution of In and Ta within BaTiO3 are systematically investigated and frequency and temperature dependent dielectric properties are reported. Experimental data indicate that doping of In and Ta within BaTiO3 follows semiconductor theory; yet, dipole substitution reduces conductivity and results in the evolution of BaTiO3 from strict ferroelectric to diffuse phase transition to a relaxor-like ferroelectric within the formed solid solution Ba(In,Ta)yTi1-2yO3, 0 ≤ y ≤ 0.0375. This work of dipole dopant substitution within BaTiO3, provides generalized guidance for developing advanced (novel) materials.

Structure and Relaxor Behavior of (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 Ternary Ceramics

Ceramics of the quasi-binary concentration section (0.1 ≤ x ≤ 0.2, Δx = 0.025) of the ternary solid solution system (0.5 − x)BiFeO3-0.5PbFe0.5Nb0.5O3-xPbTiO3 were prepared by the conventional solid-phase reaction method. An X-ray study at different temperatures revealed that (0.5 − x)BF-0.5PFN-xPT ceramics have a cluster morphology. Clusters have different modulation, crystal lattice symmetry, and chemical composition. The presence of a cluster structure in a solid solution with heterovalent substitution, consisting of regions rich in Ti+4, Nb+5, or Fe3+, has led to the appearance of Maxwell–Wagner polarization in the studied ceramics. The study of the dielectric characteristics revealed the relaxor-like behavior of the studied ceramics. The grain morphology, dielectric, pyroelectric, and piezoelectric properties of the selected solid solutions were investigated. The highest piezoelectric coefficient, d33 = 280 pC/N, was obtained in the 0.3BiFeO3-0.5PbFe0.5Nb0.5O3-0.2PbTiO3 ceramics. Study of the dielectric characteristics of all samples revealed relaxor ferroelectric behavior and a region of diffuse phase transition from the paraelectric to ferroelectric phase in the temperature range of 140–170 °C.