Fraunhofer Research Institution for Materials Recycling and Resource Strategies IWKS

Multicomponent M BCN ceramics, where M represents a transition metal, are garnering increased interest due to their multifunctionality and ultrahigh‐temperature stability. Currently, research on M BCN primarily focuses on its preparation and application in the form of thin films. In this article, we prepared monolithic BCN and HfBCN nanocomposites using a single‐source precursor approach and explored their potential application as thermoelectric materials for energy conversion. Cubic HfB x C y N 1– x – y nanocrystallites ranging from 10 to 200 nm were formed in situ within amorphous HfBCN materials after sintering at 1600°C. Furthermore, the presence of turbostratic BC x N 1– x phase within the matrix, significantly surpassing the percolation threshold, contributes to both BCN and HfBCN nanocomposites, exhibiting exceptionally high electrical conductivity exceeding 100 S cm –1 just at room temperature. A power factor of approximately 40 μW m –1 K –2 was achieved in HfBCN‐based nanocomposites, setting a record high among polymer‐derived ceramics.

SnSe compounds are studied as promising candidates for thermoelectric (TE) applications, primarily due to their remarkable achievement of a high ZT value and the relative abundance of their constituent elements. In former studies, a significant disparity in the performance of polycrystalline SnSe compounds has been observed, and the reasons for the non-reproducibility have been investigated. This study focuses on the impact of sintering temperature on the thermoelectric properties of both Br-doped and undoped SnSe materials. Through a targeted synthesis approach, we achieved a ZT value of 1.04 at T = 873 K. The results reveal a critical challenge in controlling the mobility of ions and defects for long-term application of SnSe-based thermoelectric materials. The peak ZT values observed in the initial measurements are not sustainable, as the thermoelectric performance experiences a decline during multiple heating–cooling cycles. This issue is further underscored by extended annealing experiments, which resulted in a substantial ZT decrease of approximately 50%. These outcomes emphasise the need for a comprehensive understanding of the long-term stability of SnSe materials in thermoelectric applications. Additionally, they emphasise the importance of conducting heating–cooling measurements in thermoelectric systems, particularly when aiming to achieve and maintain high ZT values for longer periods.

Abstract Collection and pre-treatment of Waste Electrical and Electronic Equipment (WEEE) are the two biggest limiting factors of enabling a high WEEE recovery rate. Small WEEE (sWEEE) have recently received increased attention by legislators that have recognised the improvement of this deficiency as an integral part of mitigating associated greenhouse-gas emissions and transforming the EU's economy towards carbon neutrality. Different sWEEE pre-treatment methods are currently in use, which pose a range of economic and ecological impacts. This study examines the economic properties and potential impacts on climate change of the different sWEEE pre-treatment options that currently exist in Germany for eight devices representative of sWEEE. A consequential bin-to-cradle life cycle assessment (cLCA) and an extended Life Cycle Costing (LCC) were conducted to identify the most beneficial pre-treatment option for each device regarding economic feasibility and greenhouse-gas emissions. The results indicate improvement potential in both aspects, particularly for the reduction of greenhouse-gas emissions, by pre-treating the device classes differently from the current status quo. Furthermore, discrepancies between most profitable and least greenhouse-gas-intensive pre-treatment option were found.

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Abstract Morphology‐controlled Cs2SbBr6 crystals are synthesized by Bi‐ and Ag‐substitution of the precursor solution. X‐ray diffraction (XRD) together with Raman spectroscopy confirms the lattice tilting and symmetry changes with the dominant appearance of higher index facets by Bi substitution. Ag substitution does not induce crystal symmetry changes in the Cs2BBr6 (B = Sb or Bi) phase, but results in highly defective structures hindering the formation of a smooth surface during the crystal growth. Successful substitution of Bi and limited substitution of Ag into Cs2SbBr6 is also confirmed by energy dispersive X‐ray spectroscopy (EDX). This research provides design principles and practical examples of how to control the morphology of Cs2SbBr6 crystals with structural defects and multiphase formation.

Abstract Dislocations in oxide ceramics significantly influence their physical properties by creating substantial local strain fields, new electronic states, and space‐charge layers. In this study, we investigated the effects of mechanically introduced dislocations on the electrical conductivity of BaTiO3 single crystals. High‐temperature plastic deformation was employed to introduce a high dislocation density with a {100}〈100〉 slip system. Impedance measurements revealed a significant anisotropy in the conductivity due to the presence of oriented dislocation structures. The crystals with dislocation lines aligned parallel to the measurement axis ([001] crystallographic direction) exhibited 16‐fold higher conductivity compared to those measured across the dislocations. Compared to the pristine crystals, this means an increase in conductivity when the measurements were carried out parallel to dislocation lines and a decrease in perpendicular measurements. Our study demonstrates that not only ferroelectric properties but also charge transport can be modified by dislocation introduction in BaTiO3.

The study of piezotronic and piezo-phototronic features in semiconducting piezoelectrics has gained considerable attention for optimizing electronic and optoelectronic device performance. In this study, we explore the photocurrent response within a ZnO varistor-type interface device and examine its UV photosensitivity enhancement through piezo-phototronic modulation of the potential barriers at grain boundaries. Doped ZnO bicrystals were synthesized using the epitaxial solid-state transformation method with polarization vectors perpendicular to the interface. The vectors can be directed both into and out of the interfaces depending on the crystallographic orientation of the crystals designated as (0001̅)|(0001̅) and (0001)|(0001) interfaces, respectively. These varistor-type boundaries demonstrate an exceptional photoelectric response to UV photons. Furthermore, our results indicate that the photoresponsivity of bicrystals with (0001)|0001 crystallographic orientation can be further enhanced under piezo-phototronic influence. Application of compressive stress of 100 MPa not only increased photocurrent formation by 1000 % but also boosted photosensitivity by 1400 %, attributed to the elevated double Schottky barrier (DSB) height at the interface resulting from mechanical loading on the bicrystal. Our findings highlight the significant role of piezoelectrically tuned potential barriers at grain boundaries in enhancing the separation and extraction of photogenerated excitons for photocurrent formation. This study introduces the engineered varistor-type interface as a promising candidate for future optoelectronic devices and contributes to our understanding of the piezo-phototronic concept in semiconductor-semiconductor interface devices.