Investigating the Thermo-Optic Properties of BCZT-Based Temperature Sensors

Photoluminescent (PL) layers and electroluminescent (EL) systems have gained significant attention for their applications in constructing flat panels, screen monitors, and lighting systems. In this study, we present a groundbreaking approach to fabricating temperature sensors using barium-calcium zirconium titanate (BCZT) with thermo-optic properties, leading to the development of opto-thermal sensors for electric vehicle battery packs. We prepared zinc sulfide (ZnS) fluorescent films on BCZT ceramics, specifically two optimal compositions, BCZT0.85 (Ba_0.85Ca_0.15Zr_0.1Ti_0.9O₃) and BCZT0.9 (Ba_0.9Ca_0.1Zr_0.1Ti_0.9O₃), via the solid-state reaction method for the dielectric layer. The BCZT powders were calcined at varying temperatures (1200 and 1250 °C) and dwell times (2 and 4 h). The resulting phase formation and microstructure characteristics were analyzed using X-ray diffraction and scanning electron microscopy, respectively. Our investigation aimed to establish a correlation between the dielectric behavior and optical properties to determine the optimal composition and conditions for utilizing BCZT as thermal detectors in electric vehicle battery packs. All BCZT powders exhibited a tetragonal phase, as confirmed by JCPDS No. 01-079-2265. We observed an increase in the dielectric constant with higher calcining temperatures or longer dwell times. Remarkably, BCZT0.85 ceramic sintered at 1250 °C for 4 h displayed the highest dielectric constant of 15,342, establishing this condition as optimal for preparing the dielectric film with a maximum dielectric constant of 42. Furthermore, we investigated the temperature-dependent electroluminescence intensity of the samples, revealing a significant enhancement with increasing temperature, reaching its peak at 80 °C. Additionally, we observed a positive correlation between electroluminescence intensity and dielectric constant, indicating the potential for improved opto-thermal sensors. The findings from this study offer promising opportunities for the development of advanced opto-thermal sensors with potential applications in electric vehicle battery packs. Our work contributes to the expanding field of photoluminescent and electroluminescent systems by providing novel insights into the design and optimization of efficient and reliable sensors for thermal monitoring in electric vehicle technologies.

Structural and Compositional Characteristics of Ball-Milled Lepidocrocite Alkali Titanate and the Correlation to Its Surface Acidic-Basic Properties

The studies on mechanical treatments of layered alkali metal oxides are limited despite their diverse compositions/structures and potential for property tuning. In this work, we vibratory mill Cs_0.7Zn_0.35Ti_1.65O₄, K_0.8Zn_0.4Ti_1.6O₄, and Cs₂Ti₆O₁₃ for up to 4 h, during which the lepidocrocite-type structure and the plate-like morphology are well preserved. X-ray diffraction (XRD) indicates a tiny (≤0.6 Å) interlayer expansion accompanied by the enhancement of the preferred orientation along the stacking direction. Chemical analyses across multiple length scales suggest Cs deintercalation, elemental redistributions, and bulk-to-surface (or crystal edge) Cs migration. This ball-milling-induced Cs-rich moiety partially blocks the surface acid sites, although the solids still show a dominating acidic character. The ball-milled samples Cs_0.7-pZn_0.35-qTi_1.65O_4-δ contain vacancies between the sheets (p) and at the sheets (q and δ). It is deduced from Sanderson's electronegativity equalization principle and experimentally verified by X-ray photoelectron spectroscopy (XPS) that ball milling increases (decreases) the partial charge at the surface acidic Ti⁴⁺/Zn²⁺ (basic O^2-) sites. These nonporous solids (≤20 m²·g^-1) contain water sorbed on the external surface as high as 1.1 mol·mol^-1, which is comparable to that in a water-intercalated sample. Our work expands the current understanding of the reactivity vs robustness in layered alkali titanates under physically demanding conditions, complementing knowledge gathered via the soft chemistry approach.