Tailoring the structure and thermoelectric properties of BaTiO3via Eu2+ substitution

A series of Ba1_xEuxTiO3_d (0.1 < x < 0.9) phases with B40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu2+ substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X-ray diffraction data only cubic perovskite structures were observed. On the local scale below about 20 \uc5 (equal to B5 unit cells) deviations from the cubic structure model (Pm%3m) were detected by evaluation of the pair distribution function (PDF). These deviations cannot be explained by a simple symmetry breaking model like in EuTiO3_d. The best fit was achieved in the space group Amm2 allowing for a movement of Ti and Ba/Eu along h110i of the parent unit cell as observed for BaTiO3. Density functional calculations delivered an insight into the electronic structure of Ba1_xEuxTiO3_d. From the obtained density of states a significant reduction of the band gap by the presence of filled Eu2+ 4f states at the top of the valence band was observed. The physical property measurements revealed that barium\u2013europium titanates exhibit n-type semiconducting behavior and at high temperature the electrical conductivity strongly depended on the Eu2+ content. Activation energies calculated from the electrical conductivity and Seebeck coefficient data indicate that at high temperatures (800 K o T o 1123 K) the conduction mechanism of Ba1_xEuxTiO3_d (0.1 r x r 0.9) is a polaron hopping when 0 o x r 0.6 and is a thermally activated process when 0.6 o x o 1. Besides, the thermal conduc tivity increases with increasing Eu2+ concentration. Due to a remarkable improvement of the power factor, Ba0.1Eu0.9TiO3_d showed a ZT value of 0.24 at 1123 K

Synthesis and Characterization of 40 wt % Ce₀.₉Pr₀.₁O₂−δ−60 wt % NdxSr₁₋ₓFe₀.₉Cu₀.₁O₃−δ Dual-Phase Membranes for Efficient Oxygen Separation

Dense, H₂- and CO₂-resistant, oxygen-permeable 40 wt % Ce₀.₉Pr₀.₁O₂–δ–60 wt % NdₓSr₁₋ₓFe₀.₉Cu₀.₁O₃−δdual-phase membranes were prepared in a one-pot process. These Nd-containing dual-phase membranes have up to 60% lower material costs than many classically used dual-phase materials. The Ce₀.₉Pr₀.₁O₂−δ–Nd₀.₅Sr₀.₅Fe₀.₉Cu₀.₁O₃−δ sample demonstrates outstanding activity and a regenerative ability in the presence of different atmospheres, especially in a reducing atmosphere and pure CO₂ atmosphere in comparison with all investigated samples. The oxygen permeation fluxes across a Ce₀.₉Pr₀.₁O₂−δ–Nd₀.₅Sr₀.₅Fe₀.₉Cu₀.₁O₃−δ membrane reached up to 1.02 mL min⁻¹ cm⁻² and 0.63 mL min⁻¹ cm⁻² under an air/He and air/CO₂ gradient at T = 1223 K, respectively. In addition, a Ce₀.₉Pr₀.₁O₂–δ–Nd₀.₅Sr₀.₅Fe₀.₉Cu₀.₁O₃–δ membrane (0.65 mm thickness) shows excellent long-term self-healing stability for 125 h. The repeated membrane fabrication delivered oxygen permeation fluxes had a deviation of less than 5%. These results indicate that this highly renewable dual-phase membrane is a potential candidate for long lifetime, high temperature gas separation applications and coupled reaction–separation processes

Effects of Cr Doping and Water Content on the Crystal Structure Transitions of Ba2In2O5

Temperature dependent crystal structure alterations in the brownmillerite type material Ba2In2O5 play a fundamental role in its applications i photocatalytic CO2 conversion; ii oxygen transport membranes; and iii proton conduction. This is connected to a reversible uptake of up an equimolar amount of water. In this study, in situ X ray and neutron diffraction were combined with Raman spectroscopy and solid state nuclear magnetic resonance experiments to unravel the effects of Cr doping and water content on the crystal structure transitions of Ba2In2O5 H2O x over a wide temperature range 10 K lt; T lt; 1573 K, x lt; 1 . A mixture of isolated and correlated protons was identified, leading to a highly dynamic situation for the protons. Hence, localisation of the protons by diffraction techniques was not possible. Cr doping led to an overall higher degree of disorder and stabilisation of the tetragonal polymorph, even at 10 K. In contrast, a further disordering at high temperatures, leading to a cubic polymorph, was found at 1123 K. Cr doping in Ba2In2O5 resulted in severe structural changes and provides a powerful way to adjust its physical properties to the respective applicatio

Multi-scale Designed CoxMn3–xO4 Spinels : Smart Pre-Catalysts towards High-Efficiency Pyrolysis-Catalysis Recycling of Waste Plastics

Acknowledgements M. W. and A. W. highly acknowledge the funding by the German Federal Ministry of Education and Research (BMBF) within the NexPlas project (project number: 03SF0618B). Y. S. Z is grateful for financial supports provided by the Royal Society of Chemistry Enablement Grant (E21-5819318767) and Royal Society of Chemistry Mobility Grant (M19-2899).Peer reviewedPostprin

Effects of Cr Doping and Water Content on the Crystal Structure Transitions of Ba₂In₂O₅

Temperature-dependent crystal structure alterations in the brownmillerite-type material Ba₂In₂O₅ play a fundamental role in its applications: (i) photocatalytic CO₂ conversion; (ii) oxygen transport membranes; and (iii) proton conduction. This is connected to a reversible uptake of up an equimolar amount of water. In this study, in situ X-ray and neutron diffraction were combined with Raman spectroscopy and solid-state nuclear magnetic resonance experiments to unravel the effects of Cr doping and water content on the crystal structure transitions of Ba₂In₂O₅(H₂O)x over a wide temperature range (10 K ≤ T ≤ 1573 K, x < 1). A mixture of isolated and correlated protons was identified, leading to a highly dynamic situation for the protons. Hence, localisation of the protons by diffraction techniques was not possible. Cr doping led to an overall higher degree of disorder and stabilisation of the tetragonal polymorph, even at 10 K. In contrast, a further disordering at high temperatures, leading to a cubic polymorph, was found at 1123 K. Cr doping in Ba₂In₂O₅ resulted in severe structural changes and provides a powerful way to adjust its physical properties to the respective application

The Fermi energy as common parameter to describe charge compensation mechanisms: A path to Fermi level engineering of oxide electroceramics

Chemical substitution, which can be iso- or heterovalent, is the primary strategy to tailor material properties. There are various ways how a material can react to substitution. Isovalent substitution changes the density of states while heterovalent substitution, i.e. doping, can induce electronic compensation, ionic compensation, valence changes of cations or anions, or result in the segregation or neutralization of the dopant. While all these can, in principle, occur simultaneously, it is often desirable to select a certain mechanism in order to determine material properties. Being able to predict and control the individual compensation mechanism should therefore be a key target of materials science. This contribution outlines the perspective that this could be achieved by taking the Fermi energy as a common descriptor for the different compensation mechanisms. This generalization becomes possible since the formation enthalpies of the defects involved in the various compensation mechanisms do all depend on the Fermi energy. In order to control material properties, it is then necessary to adjust the formation enthalpies and charge transition levels of the involved defects. Understanding how these depend on material composition will open up a new path for the design of materials by Fermi level engineering

Upcycling Waste Plastics into Multi-Walled Carbon Nanotube Composites via NiCo₂O₄ Catalytic Pyrolysis

In this work, multi-walled carbon nanotube composites (MWCNCs) were produced by catalytic pyrolysis of post-consumer plastics with aluminium oxide-supported nickel, cobalt, and their bimetallic (Ni/α–Al₂O₃, Co/α–Al₂O₃, and NiCo/α–Al₂O₃) oxide-based catalysts. The influence of catalyst composition and catalytic reaction temperature on the carbon yield and structure of CNCs were investigated. Different temperatures (800, 900, 950, and 1000°C) and catalyst compositions (Ni, Co, and Ni/Co) were explored to maximize the yield of carbon deposited on the catalyst. The obtained results showed that at the same catalytic temperature (900°C), a Ni/Co bimetallic catalyst exhibited higher carbon yield than the individual monometallic catalysts due to a better cracking capability on carbon-hydrogen bonds. With the increase of temperature, the carbon yield of the Ni/Co bimetallic catalyst increased first and then decreased. At a temperature of 950°C, the Ni/Co bimetallic catalyst achieved its largest carbon yield, which can reach 255 mg g⁻¹ plastic. The growth of CNCs followed a “particle-wire-tube” mechanism for all studied catalysts. This work finds the potential application of complex oxide composite material catalysts for the generation of CNCs in catalytic pyrolysis of wasted plastic