Ions In Lattice Research Articles

Study of Optical Properties of Non Stoichiometric Nickel Oxide

In order to create non-stoichiometric nickel oxide, the precursor was thermally decomposed at various sintering temperatures up to 1100 °C. Structure of synthesis compound was characterization by X-ray diffraction method along with ritvield refinement. In UV-visible spectroscopy the band gap of the non-stoichiometric nickel oxide due to excitation of electrons can be obtained. The presence of Ni3+ ions in the oxide lattice shows charge transfer transition, with the consequent absorption in the visible region, which is mainly due to different ratio of Ni3+ and Ni2+ ions in the sample. These data were analysed, and it was discovered that by altering the decomposition temperature, the defects present in the non-stoichiometric get held up, causing neighbouring divalent nickel ions to become Ni3+ due to charge transfer process.

Impact of nickel substitution on structural, dielectric, magnetic, and electrochemical properties of copper ferrite nanostructures for energy storage devices

Nickel-substituted copper ferrite nanoparticles (NP) (Cu1-xNixFe2O4) were prepared using a cost-effective hydrothermal method. X-ray diffraction (XRD) pattern revealed a single-phase cubic spinel structure. The increase in lattice parameters and decrease in crystallite size are associated with the replacement of Cu ions by Ni ions in the host lattice of copper ferrite. The optimized Cu0.95Ni0.05Fe2O4 composition was subsequently annealed at 750 °C and 850 °C for further studies. Fourier transform infrared (FT-IR) analysis shows the existence of two promising fundamental adsorption peaks at 465 and 582 cm−1, related to the metal ion stretching vibrations at the tetrahedral (A) and octahedral (B) sites, respectively. The local disorder at both the A and B sublattices upon the incorporation of Ni was observed from the Raman analysis. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) images shows the formation of agglomerates composed of nano-sized spherical particles. A high Barrett-Joyner-Halenda (BJH) surface area was achieved 17.25 m2/g with a particle stability of −11.1 mV obtained by the zeta potential. Both the dielectric loss and dielectric constant are decreased, whereas the AC conductivity gets increased with increasing frequency. The magnetization-field hysteresis curves exhibited ferromagnetic behavior with a pseudo-single domain, and the cyclic voltammetry study revealed a pseudocapacitive trend. This study highlights the importance of Ni substitution to control the physicochemical properties of spinel-phase CuFe2O4 for diverse applications, such as energy storage and lithium-ion batteries.

Synthesis of Al‐doped and Fe–doped ZnO nanoparticles as UV filters in sunscreens

AbstractIn this work, Al‐doped ZnO and Fe‐doped ZnO nanoparticles have been synthesized through the coprecipitation‐annealing method to create new and safer UV filters for sunscreen. The effects of metal doping on phase composition, crystal structure, surface morphology, specific surface area, and elemental composition were characterized by X‐ray diffraction, Raman spectroscopy, field emission electron scanning microscopy, nitrogen adsorption‐desorption experiments and energy‐dispersive X‐ray spectroscopy, respectively. The optical properties and photocatalytic activity of prepared powders were studied through UV‐visible diffuse reflectance spectroscopy and photocatalytic degradation of methylene blue under UV radiation. According to the experimental results, Al or Fe‐doped ZnO nanoparticles showed better UV absorption but significantly lower photocatalytic activity than the undoped ZnO sample, which enables the metal doped ZnO samples to become more effective and safer UV filter in sunscreen. The decline of photocatalytic activity can be attributed to the bulk defects caused by the insertion of Al3+ or Fe3+ ions in ZnO lattice. In particular, the sunscreen formulations using the metal doped ZnO nanoparticles display high SPF values and diverse colors changing from ivory to yellow‐brown, preventing leaving white cast on the skin, which is very suitable as sunscreen for people of color.

Multidisciplinary studies with mutated HIV-1 capsid proteins reveal structural mechanisms of lattice stabilization

HIV-1 capsid (CA) stability is important for viral replication. E45A and P38A mutations enhance and reduce core stability, thus impairing infectivity. Second-site mutations R132T and T216I rescue infectivity. Capsid lattice stability was studied by solving seven crystal structures (in native background), including P38A, P38A/T216I, E45A, E45A/R132T CA, using molecular dynamics simulations of lattices, cryo-electron microscopy of assemblies, time-resolved imaging of uncoating, biophysical and biochemical characterization of assembly and stability. We report pronounced and subtle, short- and long-range rearrangements: (1) A38 destabilized hexamers by loosening interactions between flanking CA protomers in P38A but not P38A/T216I structures. (2) Two E45A structures showed unexpected stabilizing CANTD-CANTD inter-hexamer interactions, variable R18-ring pore sizes, and flipped N-terminal β-hairpin. (3) Altered conformations of E45Aa α9-helices compared to WT, E45A/R132T, WTPF74, WTNup153, and WTCPSF6 decreased PF74, CPSF6, and Nup153 binding, and was reversed in E45A/R132T. (4) An environmentally sensitive electrostatic repulsion between E45 and D51 affected lattice stability, flexibility, ion and water permeabilities, electrostatics, and recognition of host factors.

Cu docking-activated Nb incorporation in multivariate CuO-Nb2O5/CeO2 catalysts for selective reduction of NOx with NH3

Improving the low-temperature selective catalytic reduction of NOx with NH3 (NH3-SCR) meanwhile maintaining N2 selectivity are challenging in the field of catalysis. Herein, we showcase the fabrication of the synergistic catalytic sites in the CuO-Nb2O5/CeO2 catalysts. Impressively, the CuO-Nb2O5/CeO2 is characteristic with abundant oxygen vacancies at the interfacial regions, which facilitate the redox reaction between Ce3+, Nb5+ and Cu2+ with the assistance of surface oxygen, exhibiting high NH3-SCR activity, N2 selectivity and wide temperature window at a gas hourly space velocity of 150,000 h−1. Contrast experiments, EXAFS analysis, in situ infrared and Raman spectroscopy, and theoretical calculations indicate that the introduction of proper copper ions in the CeO2 lattice induces the structure distortion of surface CeO2, improving more niobium ions incorporation into the CeO2. The embedded Nb synergizes Cu and Ce to evoke the generation of newly adsorptive sites for NOx and NH3, thus contributing to the NH3-SCR reaction.

In Situ Controlled Growth of Strongly Quantum Confined CsPbBr3/FAPbBr3 Core/Crown Nanoplatelets for Blue Light Emitting Diodes

AbstractA few unit cells of thick colloidal CsPbBr3 nanoplatelets (NPLs) exhibit strong quantum confinement. However, due to the increased surface‐to‐volume ratio, they show poor photoluminescence quantum yield (PLQY) resulting from surface traps. Here, a unique, quantum‐confined core/crown perovskite is reported for the first time, where the CsPbBr3 NPL surface is passivated by laterally grown thin FAPbBr3 crown layers. Unlike regular core/shells, the FAPbBr3 is coated around the core NPLs resulting in blue emission. Careful control of the growth kinetics while monitoring growth using in situ PL led to the formation of core/crown perovskites with nearly two times improvement in thin film PLQYs. HR‐TEM analyses show that the interplanar distances of the core match with CsPbBr3 and the crown match with FAPbBr3. The XRD and TEM analyses revealed that their thickness remains the same even if Cs+ to FA+ ratios are varied, indicating lateral growth of FAPbBr3 around the CsPbBr3 core. Further, FA+ ions in the crown lattice are confirmed by FTIR and 1HNMR. Finally, considering their high PLQYs and narrow linewidths, the core/crown NPLs are employed as blue emitters in light‐emitting diodes, and a maximum external quantum efficiency of 0.4% at 2.71 eV (457 nm) with a luminance of 513 cd m−2 is achieved.

A threefold increase in SAR performance for magnetic hyperthermia by compositional tuning in zinc-substituted iron oxide superparamagnetic nanoparticles with superior biocompatibility

In this work, we report a ultrahigh specific absorption rate (SAR) performance in Zn-substituted magnetite superparamagnetic (SPM) nanoparticles (NPs) for potential application in magnetic hyperthermia (MHT)-based cancer treatment. Although MHT shows promise in cancer therapy, challenges such as low heating performance, agglomeration of magnetic nanoparticles (MNPs) in blood veins, cytotoxicity, and hemocompatibility have hindered clinical uses. To overcome these challenges, we adopted a reverse-micelles based coprecipitation synthesis approach to prevent MNPs agglomeration and optimized the substitution of Zn ions in magnetite to enhance heating performance. Calorimetric measurements showed SAR values of 118 W/g and 181 W/g for magnetite NPs using the initial slope method (ISM) and Box Lucas method (BLM), respectively. Through our compositional optimizations, we achieved a significant increase in SAR value by consciously substituting Zn2+ ions in the magnetite lattice. Specifically, we obtained SAR values of 325 W/g and 579 W/g (>300% increase) for Zn0.3Fe2.7O4 MNPs using ISM and BLM, respectively. This enhancement can be attributed to improved saturation magnetization (174–257 kA/m) and magneto-crystalline anisotropy (12–24 kJ/m3). The increase in saturation magnetization in the magnetite MNPs can be explained by the higher magnetic moment resulting from increased Zn concentration up to ZnxFe3-xO4(x = 0.3), strengthening the JAB interaction. However, further increases in Zn concentration lead to a decrease in saturation magnetization due to non-collinearity, as described by the Yafet-Kittle model. Our optimized MNPs exhibit improved heating performance, enabling the use of lower MNPs concentrations for cancer treatment, reducing potential toxicity effects. Biocompatibility investigations demonstrated a low hemolysis rate (<5%) in a hemolysis assay with red blood cells and high cytocompatibility (>92% cell viability) in MTT assays for all compositions, confirming their potential suitability for clinical applications. This study offers a promising approach to enhance SAR performance, addressing MHT-based cancer treatment challenges, and improving clinical suitability.

Proton-controlled molecular ionic ferroelectrics

Molecular ferroelectric materials consist of organic and inorganic ions held together by hydrogen bonds, electrostatic forces, and van der Waals interactions. However, ionically tailored multifunctionality in molecular ferroelectrics has been a missing component despite of their peculiar stimuli-responsive structure and building blocks. Here we report molecular ionic ferroelectrics exhibiting the coexistence of room-temperature ionic conductivity (6.1 × 10−5 S/cm) and ferroelectricity, which triggers the ionic-coupled ferroelectric properties. Such ionic ferroelectrics with the absorbed water molecules further present the controlled tunability in polarization from 0.68 to 1.39 μC/cm2, thermal conductivity by 13% and electrical resistivity by 86% due to the proton transfer in an ionic lattice under external stimuli. These findings enlighten the development of molecular ionic ferroelectrics towards multifunctionality.

Enhanced Alkaline Hydrogen Evolution on Gd1.0/Ndx (x = 0.5, 1.0, 3.0, and 6.0%)-Doped TiO2 Bimetallic Electrocatalysts

The work reports a facile synthesis of high thermally stable nanocrystalline anatase TiO2 nanoparticles (NPs) doped with different atomic concentrations (0.5, 1.0, 3.0, and 6.0%) of Gd3+ and Nd3+ ions by a template-free and one-step solvothermal process, using titanium(IV) butoxide as a titanium precursor and dimethyl sulfoxide (DMSO) as a solvent. The structure and morphology of the Gd3+, Nd3+, and 0.5%Gd3+-0.5%Nd3+/doped TiO2 NPs have been characterized by using various analytical techniques. The Gd3+/ and Nd3+/TiO2 molar ratios were found to have a pronounced impact on the crystalline structure, size, and morphology of TiO2 NPs. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) studies revealed the proper substitution of Ti4+ by Gd3+ and Nd3+ ions in the TiO2 host lattice. The as-prepared Gdx/TiO2, Ndx/TiO2, and Gd1.0/Ndx/TiO2 bimetallic NPs, x = 0.5, 1.0, 3.0, and 6%, have been investigated as electrocatalysts for hydrogen evolution reaction (HER) in 1.0 M KOH solution using a variety of electrochemical techniques. At any doping percentage, the Gd1.0/Ndx/TiO2 bimetallic NPs showed higher HER catalytic performance than their corresponding counterparts, i.e., Gdx/TiO2 and Ndx/TiO2. Upon increasing the Nd content from 0.5 to 6.0%, the HER catalytic performance of the Gd1.0/Ndx/TiO2 bimetallic NPs was generally enhanced. Among the studied materials, the bimetallic Gd1.0/Nd6.0/TiO2 NPs emerged as the most promising catalyst with an onset potential of −22 mV vs. RHE, a Tafel slope of 109 mV dec−1, and an exchange current density of 0.72 mA cm−2. Such HER electrochemical kinetic parameters are close to those recorded by the commercial Pt/C (onset potential: −15 mV, Tafel slope: 106 mV dec−1, and exchange current density: 0.80 mA cm−2), and also comparable with those measured by the most active electrocatalysts reported in the literature. The synergistic interaction of Gd and Nd is thought to be the major cause of the bimetallic catalyst’s activity.

Semi‐Metallic Superionic Layers Suppressing Voltage Fading of Li‐Rich Layered Oxide Towards Superior‐Stable Li‐Ion Batteries

AbstractLi‐rich layered oxides (LRLOs) with greater specific capacity density are constrained by voltage attenuation and inferior rate performance because of irreversible oxygen release, metal dissolving and poor lithium‐ion transport capacity. Herein, a simple surface modification is designed to solve the performance degradation and structural collapse of LRLOs. Combining experiments with density functional theory (DFT) calculations, a semi‐metallic LiMn2O4‐like structure (LMO) with spin‐polarized conducting electrons, is introduced to the surface of the cathode restrains the activated surficial lattice oxygen ions by its stable oxygen vacancies. Additionally, Ni doping results in a fast‐ion conductor Li0.8Nb0.96Ni0.2O3structure (LNO) with lowered lithium ions diffusion barrier, which is tightly conjugating to substrate and synergistically reinforces the Li diffusion path through the cathode‐electrolyte interphase. Moreover, Mn dissolution is successfully relieved due to the decrease in Mn concentration in the coating layers. As a result, the modified material (LRLO@LMO@LNO) exhibits an ultra‐high discharge capacity of 120.4 mAh g−1even at 10 C with a very small discharge voltage attenuation of 313 mV after 600 cycles (0.52 mV per cycle) at 1 C. Undoubtedly, this method discloses a simple and effective approach to promote the practical utilization of high‐energy‐density.

Semi-Metallic Superionic Layers Suppressing Voltage Fading of Li-Rich Layered Oxide Towards Superior-Stable Li-Ion Batteries.

Li-rich layered oxides (LRLOs) with greater specific capacity density are constrained by voltage attenuation and inferior rate performance because of irreversible oxygen release, metal dissolving and poor lithium-ion transport capacity. Herein, a simple surface modification is designed to solve the performance degradation and structural collapse of LRLOs. Combining experiments with density functional theory (DFT) calculations, a semi-metallic LiMn2 O4 -like structure (LMO) with spin-polarized conducting electrons, is introduced to the surface of the cathode restrains the activated surficial lattice oxygen ions by its stable oxygen vacancies. Additionally, Ni doping results in a fast-ion conductor Li0.8 Nb0.96 Ni0.2 O3 structure (LNO) with lowered lithium ions diffusion barrier, which is tightly conjugating to substrate and synergistically reinforces the Li diffusion path through the cathode-electrolyte interphase. Moreover, Mn dissolution is successfully relieved due to the decrease in Mn concentration in the coating layers. As a result, the modified material (LRLO@LMO@LNO) exhibits an ultra-high discharge capacity of 120.4 mAh g-1 even at 10 C with a very small discharge voltage attenuation of 313 mV after 600 cycles (0.52 mV per cycle) at 1 C. Undoubtedly, this method discloses a simple and effective approach to promote the practical utilization of high-energy-density.

Stable oxygen permeable membrane with Ce0.9Gd0.1O2-δ protective layer for syngas production

The stability of catalytic membrane reactors (CMRs) is crucial for the practical applications in chemical reaction processes. However, currently reported CMRs with perovskite-based oxygen permeable membranes usually show poor stability owing to the over-reduction of Co and Fe ions in perovskite lattice under harsh reducing gas atmospheres and the interaction between membrane and catalyst. Here we developed an oxygen permeable membrane Ce0.9Gd0.1O2-δ-SrCe0.5Fe0.5O3-δ (CGO-SCF) with Ce0.9Gd0.1O2-δ (CGO) protective layer to construct a catalytic membrane reactor packed with Ni/Al2O3 catalyst for partial oxidation of methane. The CGO dense protective layer can effectively avoid the over-reduction of Fe ions in perovskite under harsh reducing gas atmospheres and the interaction between perovskite and Ni/Al2O3. Benefiting from high stability and mixed ionic-electronic conductivity of CGO in a low oxygen partial pressure environment, the developed membrane reactor with a dense CGO thin film was successfully operated with a stable CH4 conversion of 87% and a H2/CO ratio of 2 over 200 h in harsh operating conditions. This strategy proposed here provides insights into the design of highly stable catalytic membrane reactor in harsh conditions.

Magnetic anisotropy in the ferromagnetic Mn and N doped ZnO Nanocrystals

(Mn, N)- codoped ZnO thin films were prepared by two step process. Study of Magnetic anisotropy in Mn and N codoped ZnO nanoparticles was studied. X-ray diffraction (XRD) &X-ray photoelectron spectroscopy (XPS) reveals that Manganese (Mn) and Nitrogen (N) ions in ZnO lattice exists as Mn2+ and N3-. Hysteresis measurement shows that at room temperature the samples show ferromagnetic nature and also indicate that the samples are having magnetic anisotropic behavior. This ferromagnetic nature in the samples is because of the hybridization between 2p of N & 3d of Mn state. The compound formed, corresponds to Mn-N-Mn cluster, which is found to be energetically strong enough for ferromagnetism at room temp.

Sm doped ZnO-SnO2 nanocomposites with improved photo-degradation strength and antibacterial properties

In this work, we devoted our effort to synthesize rare-earth (Sm3+) doped ZnO-SnO2 nanocomposites by sol-gel method to address issues like wastewater treatment and minimization of bacterial infection. Successful formation of multi-phase nanocomposites of hexagonal ZnO and tetragonal SnO2 has been confirmed by x-ray diffraction (XRD) analysis. The effect of Sm doping is understood from the enhancement in ZnO grain growth and shift in diffraction peaks. The morphology study by FESEM reveals the variation in sample morphology with Sm doping with energy-dispersive analysis of x-ray (EDAX) study providing the confirmation on the existence of Sm ions in the crystal lattice of ZnO-SnO2 heterostructure. Transmission electron microscopic (TEM) study manifests the formation of two distinct types of particles (hexagonal & spherical) corresponding to ZnO and SnO2 which has been further clarified from the measurement of lattice spacing from the high-resolution TEM images and indexing of selected area electron diffraction (SAED) pattern. The near band edge emission (NBE) of ZnO is blue shifted along with the evolution of oxygen vacancy defects which induced new bands at 488 nm and 613 nm upon Sm doping. Further, intra-4f transitions of Sm3+ ions have also been observed at 560 nm, 590 nm and 638 nm linked to 4G5/2– 6HJ (J = 5/2, 7/2, 9/2) transitions. The Zn, Sn, O, and Sm elements are confirmed to exist in the nanocomposite according to the X-ray photoelectron spectroscopy (XPS) investigation which provided information on the chemical composition and electronic states of the material. Photocatalytic degradation study of toxic environmental dyes like methylene blue (MB), Congo red (CR) and methyl orange (MO) shows that Sm3+ ions in ZnO/SnO2 helps to enhance the degradation efficiency by the formation of Z-scheme heterojunctions between ZnO and SnO2. This allows the delay in recombination rate of the photoinduced electron/hole pairs. The antibacterial behavior of the prepared nanocomposites against E. Coli and S. Aureus has also been studied in detail which demonstrates improved antibacterial efficiency of the samples.

Quantum anomalous Hall insulator in ionic Rashba lattice of correlated electrons

Quantum anomalous Hall insulator in ionic Rashba lattice of correlated electrons

Unraveling segregation behavior of inactive secondary phase driven by ion-competition reaction for perovskite-2D PbI2 heterojunction solar cells

The undesired segregation of inactive secondary phase that randomly distributed across the perovskite film is detrimental to charge-carrier transport dynamics and light stability. However, in-depth studies for understanding the underlying chemical reaction mechanism and the relationship between phase structural configuration and physical properties are still lacking. Herein, the segregation behavior of the inactive secondary phase and the underlying microcosmic mechanism regarding ionic chemical replacement reaction and lattice reconfiguration process are systematically elaborated. A high-quality perovskite-PbI2 heterojunction film is constructed via converting the three-dimensional PbI2 photoactive phase into a two-dimensional inactive phase, alleviating the energetic disorder of carrier dynamics and photochemical dissociation. The resultant perovskite solar cells achieve an efficiency of 24.23% with excellent light-resistance. The dissociation energetics of phase dimensional structure is theoretically analyzed. This work provides new insights into crystal structure design for constructing high-quality perovskite heterojunction devices.

Triplet States of Cyanostar and Its Anion Complexes.

The design of advanced optical materials based on triplet states requires knowledge of the triplet energies of the molecular building blocks. To this end, we report the triplet energy of cyanostar (CS) macrocycles, which are the key structure-directing units of small-molecule ionic isolation lattices (SMILES) that have emerged as programmable optical materials. Cyanostar is a cyclic pentamer of covalently linked cyanostilbene units that form π-stacked dimers when binding anions as 2:1 complexes. The triplet energies, ET, of the parent cyanostar and its 2:1 complex around PF6- are measured to be 1.96 and 2.02 eV, respectively, using phosphorescence quenching studies at room temperature. The similarity of these triplet energies suggests that anion complexation leaves the triplet energy relatively unchanged. Similar energies (2.0 and 1.98 eV, respectively) were also obtained from phosphorescence spectra of the iodinated form, I-CS, and of complexes formed with PF6- and IO4- recorded at 85 K in an organic glass. Thus, measures of the triplet energies likely reflect geometries close to those of the ground state either directly by triplet energy transfer to the ground state or indirectly by using frozen media to inhibit relaxation. Density functional theory (DFT) and time-dependent DFT were undertaken on a cyanostar analogue, CSH, to examine the triplet state. The triplet excitation localizes on a single olefin whether in the single cyanostar or its π-stacked dimer. Restriction of the geometrical changes by forming either a dimer of macrocycles, (CSH)2, or a complex, (CSH)2·PF6-, reduces the relaxation resulting in an adiabatic energy of the triplet state of 2.0 eV. This structural constraint is also expected for solid-state SMILES materials. The obtained T1 energy of 2.0 eV is a key guide line for the design of SMILES materials for the manipulation of triplet excitons by triplet state engineering in the future.

Thermal and thermoelectric properties of zinc oxide ceramics alloyed with metals

The paper studies the thermal, electrical and thermoelectric properties of ZnO–MexOy ceramics with 1 ≤ x, y ≤ 3, where Me = Al, Co, Fe, Ni, Ti. The samples were made on the basis of ceramic sintering technology of powder mixtures of two or more oxides in an open atmosphere with variations in temperature and duration of annealing. Structural and phase studies of ceramics indicate that the addition of powders of MexOy alloying agents to ZnO powder with a wurtzite structure after the synthesis process leads to the release of secondary phases such as Znx(Me)yO4 spinels and a 4-fold increase in the porosity of the resulting ceramics. Studies of thermal conductivity at room temperature indicate the predominance of the lattice contribution. The decrease in thermal conductivity during doping is due to an increase in phonon scattering due to the influence of the following factors: (1) the size factor when replacing zinc ions in the ZnO (wurtzite) crystal lattice with metal ions from the added MexOy oxides; (2) the formation of defects – point, grain boundaries (microstructure grinding); (3) increase in porosity (decrease in density); and (4) formation of additional phase particles (such as spinels Znx(Mе)yO4). The effect of these factors in the substitution of zinc ions with metals (Co, Al, Ti, Ni, Fe) leads to an increase in the thermoelectric Q-factor of ZT by 4 orders of magnitude (due to a decrease in electrical resistivity and thermal conductivity with a relatively small decrease in the coefficient of thermal EMF). The reason for the decrease in electrical resistance is the more uniform redistribution of alloying metal ions in the wurtzite lattice, resulting in an increase in the number of donor centers, formed with an increase in the duration of annealing.

Thermal and thermoelectric properties of metal-doped zinc oxide ceramics

The thermal, electrical and thermoelectric properties of ZnO–MexOy ceramics with 1 ≤ x, y ≤ 3, where Me = Al, Co, Fe, Ni, Ti, have been studied. The specimens have been synthesized using the ceramic sintering technology from two or more oxides in an open atmosphere with annealing temperature and time variation. The structural and phase data on the ceramics have shown that post-synthesis addition of MexOy doping powders to wurtzite-structured ZnO powder causes Znx (Mе)yO4 spinel-like second phase precipitation and a 4-fold growth of ceramics porosity. Room temperature heat conductivity studies have testified to predominant lattice contribution. A decrease in the heat conductivity upon doping proves to be caused by phonon scattering intensification due to the following factors: size factor upon zinc ion substitution in the ZnO lattice (wurtzite) by MexOy doping oxide metal ions; defect formation, i.e., point defects, grain boundaries (microstructure refinement); porosity growth (density decline); secondary phase particle nucleation (Znx (Mе)yO4 spinel-like ones). The above listed factors entailed by zinc ion substitution for metal ions (Co, Al, Ti, Ni, Fe) increase the figure-of-merit ZT by four orders of magnitude (due to a decrease in the electrical resistivity and heat conductivity coupled with a moderate thermo-emf decline). The decrease in the electrical resistivity originates from a more homogeneous distribution of doping metal ions in the wurtzite lattice upon longer annealing which increases the number of donor centers.

Influence of single-ionized oxygen vacancies on the generation of ferromagnetism in SnO2 and SnO2:Cr nanowires

In this work, we report the influence of single-ionized oxygen vacancies (V^{prime}_{{text{O}}}) as a spin ½ system in the ferromagnetic response of undoped and Cr-doped SnO2 nanowires. For this study, undoped and Cr-doped SnO2 nanowires were synthesized by a thermal evaporation method. Raman, Auger, and X-ray photoelectron spectroscopies confirmed the incorporation of Cr3+ ions in the SnO2 lattice. Electron paramagnetic resonance measurements demonstrated the presence of single-ionized oxygen vacancies (V^{prime}_{{text{O}}}) in undoped and Cr-doped nanowires. Complementarily, cathodoluminescence measurements confirmed the presence of VO defects in the samples. Magnetic measurements revealed FM behavior from the undoped SnO2 and Cr-doped SnO2 nanowires, showing magnetization saturation values (MS) of ± 1 × 10–3 and ± 1.6 × 10–3 emu/g, respectively, and magnetic coercivity values (HC) of 180 and 200 Oe. We assign the FM response of nanowires to the presence of single ionized V^{prime}_{{text{O}}} acting as a spin ½ system and to the alignment of magnetic moments of Cr3+ ions, finding that V^{prime}_{{text{O}}} defects dominate in the FM generation.