Neamul Hayet Khansur

Sr _x La _{2– x} NiMnO ₆ , a bi-functional adsorbent and photocatalyst for trypan blue adsorption with UV-driven in situ regeneration, enabling adsorbent reuse.

This study examines the dielectric and elastic properties of aluminate sodalite‐type oxides Ca ₈ [(Al _{1− x} Ga _x )O ₂ ] ₁₂ {WO ₄ } ₂ ( x = 0.00, 0.05, and 0.10) to elucidate their complex phase‐transition behavior. Combined dielectric and elastic measurements reveal successive transitions from a paraelastic high‐temperature phase to a ferroelastic low‐temperature phase through intermediate ferroelastic phases. For x = 0.00, two intermediate phases emerge during cooling, whereas only one is observed upon heating, indicating an asymmetric transition pathway. Increasing Ga content progressively destabilizes and ultimately suppresses the intermediate phase, likely due to enhanced entropy effects. Broad dielectric and elastic anomalies observed below 500 K for x = 0.00 suggest the formation of polar nanoclusters, whose disappearance upon Ga substitution coincides with the loss of the intermediate phase. These findings have clarified composition–structure–property relationships in Ca ₈ [(Al _{1− x} Ga _x )O ₂ ] ₁₂ {WO ₄ } ₂ and provided insights into the design of functional properties in aluminate sodalite‐type oxides.

Porous freeze-cast ferroelectric ceramics are attractive for piezoelectric sensors and energy harvesters owing to their enhanced functional properties compared to monolithic ceramics. While the effects of the cooling rate during freeze-casting on the microstructure and mechanical properties of various oxides have been studied, this paper is the first to explore how it influences the microstructure–functional properties relationships of porous ferroelectric lead zirconate titanate. Freeze-casting cooling rates of 1–4 °C/min were investigated, and the microstructure and electromechanical properties were analyzed, informed using finite element modeling. Increasing the cooling rate from 1 to 4 °C/min reduced the effective ceramic wall thickness from 34.9 ± 8.8 μm to 14.4 ± 4.4 μm, enhanced the degree of ceramic alignment, and reduced the number of wall defects (i.e., pores within ceramic walls). These microstructural improvements led to enhanced and more consistent piezoelectric charge coefficients, d33, from 274 ± 111 pC/N at 1 °C/min to 324 ± 31 pC/N at 4 °C/min. The compressive strength of the porous PZT was also enhanced with higher cooling rates during freeze-casting, increasing from 12.3 ± 5.5 MPa to 72.1 ± 9.2 MPa. Materials fabricated using higher cooling rates exhibited greater thermal stability near the Curie point. Finite element simulations revealed that thin-walled structures led to reduced mechanical clamping and enhanced polarization under applied electric fields, thereby contributing to higher d33. These results are key optimization parameters for fabricating advanced piezoelectric composites with enhanced and reliable properties for energy harvesting, sonar, and sensing applications, while minimizing industrial waste.

Three-step workflow that links stress state evaluation to stress-guided design in solid-state ionic devices. Multilength scale characterization of chemo-mechanical coupling.

The domain structure of Sn-doped BaTiO ₃ was examined with piezoresponse force microscopy and spatially resolved Raman spectroscopy, and derived reversible and irreversible contributions from Rayleigh analysis of the dielectric response.

The increasing demand for efficient, multifunctional energy conversion systems has sparked interest in light‐active polar perovskite oxides. These materials offer structural flexibility and chemical tunability, making them promising candidates for multimodal energy harvesting. In particular, photoferroelectrics enable the simultaneous harvesting of thermal, light, and mechanical energy. However, mostly room temperature properties have been studied, leaving a critical gap in understanding their behavior under varying thermal conditions. This study investigates the electromechanical properties in conjunction with crystallographic changes of photoferroelectric BaTi ₁ ₋ _x Sn _x O ₃ across a temperature range of −150°C to 150°C. Increasing Sn content reduces tetragonal distortion, shifts phase transition temperatures, and induces a multi‐phase region at higher concentrations. As a result, temperature‐dependent small‐signal measurements show changes in dielectric and piezoelectric responses, with a trend toward relaxor‐like behavior at higher Sn levels. Rayleigh analysis of stress amplitude‐dependent piezoelectric coefficient reveals enhanced properties at specific compositions, for example, 7 mol% Sn) and temperatures, attributed to an optimal balance of reversible and irreversible contributions. Further, Sn doping appears to improve thermal stability by reducing irreversible contributions. These results provide significant implications for optimizing photoferroelectric BaTiO ₃ by influencing material properties through Sn doping for various applications, including energy harvesting.

To meet the growing demand for energy, multimodal energy conversion systems, such as photoferroelectrics, are receiving increased attention. Among these, oxide perovskites like Sn substituted barium titanate exhibit enhanced piezoelectric coefficient and dielectric permittivity at room temperature compared to the parent composition. This study investigates whether these enhancements originate from intrinsic Sn incorporation or extrinsic contributions. Additionally, the impact of Sn on the electronic bandgap is examined, which is critical for multifunctional applications. A combined experimental and first-principles approach is employed to systematically analyze different Sn concentrations (0–12.5 mol. % Sn), focusing on B-site ordering in BaTiO3. The experimental analysis includes dielectric and ferroelectric measurements, diffuse reflectance spectroscopy, and photoconductivity measurements for bandgap estimations. Computational screening reveals that Sn ions repel each other and preferentially adopt second neighbor B-site positions along the Ti–O–Ti bond. While the bandgap shows minimal changes (meV range), spontaneous polarization and polarization hysteresis decrease significantly with increasing Sn content. The experimentally observed increase in piezoelectric response is thus attributed primarily to extrinsic effects on the meso- and macroscales from the domain structure and the coexistence of phases around 11 mol. % Sn, rather than to intrinsic incorporation of Sn into the perovskite lattice.

Despite the extraordinary significance of high-temperature piezoelectric ceramics in engineered systems, understanding their macroscopic electromechanical response in terms of local underlying phenomena, in particular the domain dynamics at elevated temperatures that directly influence the stability of device performance, remains a significant challenge. Here, we investigate the relationship between domain evolution with temperature and its piezoelectric response utilizing 0.7Bi_1.05FeO₃–0.3BaTiO₃ (BF30BT), a critical alternative to lead-based ferroelectrics for high-temperature applications. By analyzing the frequency and loading amplitude-dependent Rayleigh behavior, we are able to demonstrate the importance of the intrinsic contributions in piezoelectric response. The re-entrant relaxor nature of BF30BT results in active locally heterogeneous nanodomains that display reversible rapid response contributions rather than typical extrinsic contributions due to their low activation energy. Decoding the complicated domain dynamics of BF30BT allows for the further integration of microstructures and macroscopic characteristics, guiding the design and utilization of further high-temperature piezoelectric ceramics.

Dislocations are being used to tune versatile mechanical and functional properties in oxides with most current studies focusing on single crystals. For potentially wider applications, polycrystalline ceramics are of concern, provided that dislocations can be successfully introduced. However, in addition to preexisting pores and flaws, a major barrier for bulk plastic deformation of polycrystalline ceramics lies in the grain boundaries (GBs), which can lead to dislocation pile‐up and cracking at the GBs due to the lack of sufficient independent slip systems in ceramics at room temperature. Here, we use the cyclic Brinell indentation method to circumvent the bulk deformation and focus on near‐surface regions to investigate the plastic deformation of polycrystalline SrTiO₃ at room temperature. Dislocation etch‐pit analysis suggests that plastic deformation can be initiated within the grains, at the GBs, and from the GB triple junction pores. The deformability of the individual grains is found to be dependent on the number of cycles, as also independently evidenced on single‐crystal SrTiO₃ with representative surface orientations (001), (011), and (111). We also identify a grain‐size‐dependent plastic deformation.