Electrical and Optical Properties of CaTi1-yFeyO3-δ Perovskite Films as Interlayers for Optoelectronic Applications.

CaTi1-yFey O3-δ perovskite oxide films are promising candidate materials for p-type interlayers of third generation solar cells or light-emitting devices. The impact of atomic Ti substitutions by Fe on electrical and optical properties of CaTi0.5Fe0.5O3-δ perovskite films have been studied. The best compromise between a high transmission coefficient and the suitable electrical conductivity is obtained for a specific atomic composition of Ca (1) Ti (0.5) Fe (0.5) O (3-δ) perovskite films. This paper shows that CaTi1-yFeyO3-δ perovskite oxides can be integrated as p-type interfacial layers of optoelectronic devices through their work functions, electrical, and optical properties.

Investigation of Electrical Transitions in the First Steps of Spark Plasma Sintering: Effects of Pre-Oxidation and Mechanical Loading within Copper Granular Media.

Spark Plasma Sintering (SPS) has become a conventional and promising sintering method for powder consolidation. This study aims to well understand the mechanisms of densification encountered during SPS treatments, especially in the early stages of sintering. The direct current (DC) electrical behavior of copper granular medium is characterized. Their properties are correlated with their microstructural evolutions through post-mortem scanning electron microscope (SEM) observations to allow a thorough understanding of the involved Branly effect that is suspected to occur in SPS. The electrical response is studied by modifying the initial thickness of the oxide layer on particles surfaces and applying various mechanical loads on the granular medium. Without load and at low current, the measured quasi-reversible behavior is connected to the formation of spots at the microcontacts between the particles. By increasing the current, the Branly transition from an insulating to a conductive state suddenly occurs. The insulating oxide layer is destroyed, and micro-bridges are created. The application of a mechanical pressure strongly modifies the DC Branly effect. Increasing low stress leads to a strong decrease in the breakdown field. For high-applied pressure, successive drops in the electric field are detected during the electrical transition. These successive drops are induced by microcracking of the insulating oxide layer.

High permittivity processed SrTiO3 for metamaterials applications at terahertz frequencies.

High permittivity SrTiO3 for the realization of all-dielectric metamaterials operating at terahertz frequencies was fabricated. A comparison of different processing methods demonstrates that Spark Plasma Sintering is the most effective sintering process to yield high density ceramic with high permittivity. We compare this sintering process with two other processes. The fabricated samples are characterized in the low frequency and in the terahertz frequency ranges. Their relative permittivities are compared with that of a reference SrTiO3 single crystal. The permittivity of the sample fabricated by Spark Plasma Sintering is as high as that of the single crystal. The role of the signal-to-noise ratio in the measurements at terahertz frequency is detailed.