arXiv subjects

Andrea Giunto

Publications and source records attributed to Andrea Giunto.

4 recordsLinked to original sources

arXiv2025

Synthetic accessibility and sodium ion conductivity of the Na$_{8-x}$A$^{x}$P$_2$O$_9$ (NAP) high-temperature sodium superionic conductor framework

Advancement of solid state electrolytes (SSEs) for all solid state batteries typically focuses on modification of a parent structural framework for improved conductivity, \textit{e.g.} cation substitution for an immobile ion or varying the concentration of the mobile ion. Therefore, novel frameworks can be disruptive by enabling fast ion conduction aided by different structure and diffusion mechanisms, and unlocking optimal conductors with different properties (\textit{e.g.} mechanical properties, sintering needs, electrochemical stability) than previously published. Herein, we perform a high throughput survey of an understudied structural framework for sodium ion conduction, Na$_{8-x}$A$^x$P$_2$O$_9$ (NAP), to understand the family's thermodynamic stability, synthesizability, and ionic conduction. We first show that the parent phase Na$_4$TiP$_2$O$_9$ (NTP) undergoes a structural distortion (with accompanying conductivity transition) due to unstable phonons from a pseduo-Jahn Teller mode in the 1D titanium chains. Then, screening of cation-substituted structural candidates with \textit{ab initio} and machine-learned potential calculations reveal a number of candidates that are thermodynamically stable, likely synthesizable, and have high predicted ionic conductivities. High throughput experimental trials and subsequent methodology optimization of one Na$_4$SnP$_2$O$_9$ (NSP) highlight collective challenges to the synthesis pathways for sodium phosphate materials via solid state synthesis. Our results demonstrate that NAP is a highly tunable conduction framework whose high temperature conductivity transition has heretofore eliminated it from significant research interest. By expanding the structural toolkit for SSE design, we increase the number of useful sodium ion electrolytes for integration into safe and accessible solid state batteries.

cond-mat.mtrl-sci↗

arXiv2024

GeSn Defects and their Impact on Optoelectronic Properties: A Review

GeSn has emerged as a promising semiconductor with optoelectronic functionality in the mid-infrared, with the potential of replacing expensive III-V technology for monolithic on-chip Si photonics. Multiple challenges to achieve optoelectronic-grade GeSn have been successfully solved in the last decade. We stand today on the brink of a potential revolution in which GeSn could be used in many optoelectronic applications such as Light Detection and Ranging (LiDARs) devices and lasers. However, the limited understanding and control of material defects represents today a bottleneck in the performance of GeSn-based devices, hindering their commercialisation. Point and linear defects in GeSn have a strong impact on its electronic properties, namely unintentional doping concentration, carrier lifetime and mobility, which ultimately determine the performance of optoelectronic devices. In this review, after introducing the state-of-the-art of the fabrication and properties of GeSn, we provide a comprehensive overview of the current understanding of GeSn defects and their influence on the material (opto)electronic properties. Throughout the manuscript, we highlight the critical points that are still to solve. By bringing together the different fabrication techniques available and characterizations realized we provide a wholistic view on the field of GeSn and provide elements on how it could move forward.

physics.app-ph↗

arXiv2023

Surfactant behavior and limited incorporation of Indium during in-situ doping of GeSn grown by MBE

GeSn is a promising group-IV semiconductor material for on-chip Si photonics devices and high-mobility transistors. These devices require the use of doped GeSn regions, achieved preferably in-situ during epitaxy. From the electronic valence point of view, p-type dopants of group-IV materials include B, Al, Ga and In. The latter element has never been investigated as p-type dopant in GeSn. In this work, we explore in-situ In p-type doping of GeSn grown by MBE. We demonstrate that In acts as a surfactant during epitaxial growth of GeSn:In, accumulating on surface and inducing segregation in the form of mobile Sn-In liquid droplets, strongly affecting the local composition of the material. In non-defective GeSn, we measure a maximal In incorporation of 2.8E18cm-3, which is two orders of magnitude lower than the values reported in the literature for in-situ p-type doping of GeSn. We further show that In induces the nucleation of defects at low growth temperatures, hindering out-of-equilibrium growth processes for maximization of dopant incorporation. This work provides insights on the limitations associated with in-situ In doping of GeSn, and discourages its utilization in GeSn-based optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2022

Understanding the growth mechanism of BaZrS$_3$ chalcogenide perovskite thin films from sulfurized oxide precursors

Barium zirconium sulfide (BaZrS3) is an earth-abundant and environmentally friendly chalcogenide perovskite with promising properties for various energy conversion applications. Recently, sulfurization of oxide precursors has been suggested as a viable solution for effective synthesis, especially from the perspective of circumventing the difficulty of handling alkali earth metals. In this work, we explore in detail the synthesis of BaZrS3 from Ba-Zr-O oxide precursor films sulfurized at temperatures ranging from 700 °C to 1000 °C. We propose a formation mechanism of BaZrS3 based on a two-step reaction involving an intermediate amorphization step of the BaZrO3 crystalline phase. We show how the diffusion of sulfur (S) species in the film is the rate-limiting step of this reaction. The processing temperature plays a key role in determining the total fraction of conversion from oxide to sulfide phase at a constant flow rate of the sulfur-containing H2S gas used as a reactant. Finally, we observe the formation of stoichiometric BaZrS3 (1:1:3), even under Zr-rich precursor conditions, with the formation of ZrO2 as a secondary phase. This marks BaZrS3 quite unique among the other types of chalcogenides, such as chalcopyrites and kesterites, which can instead accommodate quite a large range of non-stoichiometric compositions. This work opens up a pathway for further optimization of the BaZrS3 synthesis process, straightening the route towards future applications of this material.

cond-mat.mtrl-sci↗