arXiv subjects

Pascal Andreazza

Publications and source records attributed to Pascal Andreazza.

3 recordsLinked to original sources

arXiv2026

Consistent transition model for Bi0.5Na0.5TiO3 from temperature-dependent structural and electrical properties

BNT based solid solutions are promising parent materials for lead free dielectric capacitors, thanks to their high recoverable energy densities and breakdown strengths. However, the ambient temperature symmetry and high temperature phase evolution of BNT remain unclear. Crucially, structural transformations and electrical ordering are most often considered independently, hindering a coherent understanding of the BNT phase transition. In this work, we combine X ray diffraction, transmission electron microscopy, Raman spectroscopy, impedance spectroscopy, and high field polarization cycling to establish a unified picture of the structural and dielectric response of BNT. Based on these results, we propose a consistent transition model for BNT that reconciles previously conflicting interpretations. This integrated structure property study provides a rationale for developing high performance, lead free energy storage materials.

cond-mat.mtrl-sci↗

arXiv2024

Enhancement of piezoelectric properties in a narrow cerium doping range of $\text{Ba}_{1-x}\text{Ca}_{x}\text{Ti}_{1-y}\text{Zr}_{y}\text{O}_{3}$ evidenced by high throughput experiment

Lead-free materials based on the $\text{(Ba,Ca)(Zr,Ti)O}_{3}$ (BCZT) system exhibit excellent electromechanical properties that can be strongly modified by small amounts of dopants. Here, we use a high throughput strategy to unravel the influence of aliovalent doping with Ce on dielectric and piezoelectric properties of BCTZ. We synthesize and characterize a single BCTZ thin film with a composition gradient from undoped to 0.2 mol % cerium doping. The cerium doping increases the piezoelectric coefficient from $42.3\pm 2.9 \text{pm V}^{-1}$ (undoped) to $63\pm 2.4 \text{pm V}^{-1}$ for 0.06 Ce-mol\%, and then decreases to $38.4 \pm 1.3 \text{pm V}^{-1}$ for the maximum amount of cerium (0.2 mol %). An investigation of sub-coercive field non-linearities reveal that these variations are not only induced by changes in dynamics and densities of domain walls. The results highlight the advantage of high throughput techniques to identify ideal compositions for applications, without synthesizing a high number of samples with unavoidable sample-to-sample variations.

cond-mat.mtrl-sci↗

arXiv2023

Subcoercive-field dielectric response of $0.5(\text{Ba}_{0.7}\text{Ca}_{0.3}\text{TiO}_{3})-0.5(\text{BaZr}_{0.2}\text{Ti}_{0.8}\text{O}_{3})$ thin film: peculiar third harmonic signature of phase transitions and residual ferroelectricity

Sub-coercive field non-linearities in $0.5(\text{Ba}_{0.7}\text{Ca}_{0.3}\text{TiO}_{3})-0.5(\text{BaZr}_{0.2}\text{Ti}_{0.8}\text{O}_{3})$ (BCTZ 50/50) thin film elaborated using pulsed laser deposition are studied using permittivity and phase angle of the third harmonic measurements as function of the AC measuring field $E_{\mathit{AC}}$ and temperature. The global phase transition temperature $T_{\mathit{max}}$ for which the permittivity is maximum, decreases from 330 K to 260 K when $E_{\mathit{AC}}$ increases. Rayleigh analysis of the AC field dependence of the relative permittivity shows a regular decrease of the domain wall motion contributions as temperature increases up to $T_{\mathit{max}}$ and an even more pronounced decrease above $T_{\mathit{max}}$. This measurement reveals that the ferroelectric behavior subsists 70 K above the global phase transition. The phase angle of the third harmonic at temperatures below 275 K, is characteristic of a conventional ferroelectric and from 275 K to $T_{\mathit{max}}=$ 330 K of a relaxor. Above $T_{\mathit{max}}$, the thin film exhibits a peculiar phase angle of the third harmonic, which consists of ${-180}{\deg}\rightarrow {-225}{\deg}\rightarrow {+45}{\deg} \rightarrow {0}{\deg}$ instead of the ${-180}{\deg}\rightarrow {-90}{\deg} \rightarrow {0}{\deg}$ found for relaxor. This peculiar behavior is observed only on heating, and is tentatively attributed to changes in the correlations between polar nanoregions.

cond-mat.mtrl-sci↗