Ferromagnetism in Li doped ZnO nanoparticles: The role of interstitial Li

ZnO nanoparticles doped with Li (Zn1−yLiyO, y ≤ 0.1) have been investigated with emphasis on the correlation between their magnetic, electronic, and structural properties. In particular, defects such as interstitial Li and Zn atoms, substitutional Li atoms, and oxygen vacancies have been identified by X-ray photoelectron spectroscopy(XPS) and their respective roles in stabilization of the magnetic moment are discussed. X-ray diffraction(XRD) and XPS give clear evidence of Li presence at both substitutional and interstitial sites. XPS studies further show that the amount of substitutional Li defects (Lizn) and interstitial Li defects (Lii) vary non-monotonically with the Li concentration, with the Lii defects being noticeably high for the y = 0.02, 0.08, and 0.10 concentrations, in agreement with the XRD results. Magnetization studies show room temperature ferromagnetism in these nanoparticles with the moment being largest for the particles with high concentration of interstitial lithium and vice versa. Both interstitialZn(Zni) defects and Zn-O bonds were determined from the Zn LMM Auger peaks; however, the variation of these with Li concentrations was not large. Oxygen vacancies (Vo) concentrations are estimated to be relatively constant over the entire Li concentration range. We relate the Lii and Zni defects to the formation and stabilization of Znvacancies and thus stabilizing the p-type ferromagnetism predicted for cation (zinc)vacancy in the ZnO type oxides

Investigation of phase evolution and control over phase transformation temperature and thermal hysteresis using stoichiometry and co-doping in VO2 thin films

Structural phase transition temperature and its associated hysteresis in VO2 have been controlled by high valent dopant induced local structural modification which acts as phase nucleation site during phase transformation. Monoclinic phase intensity loops plotted against temperature has been observed to exhibit thermal hysteresis. It is shown that the size, shape and central position of hysteresis loop depend on stoichiometry and doping concentration. Highest reduction in phase transformation temperature and thermal hysteresis width has been observed in case of W+6-Mo+6 co-doping and W+6 doping, respectively. Hence energy barrier associated with the structural phase transition has been successfully manipulated to vary Tc and hysteresis width. These findings have implications for designing the phase switching devices and smart window applications

Synthesis and characterization of ZnGa2O4 particles prepared by solid state reaction

We employed solid state reaction technique to synthesize ZnGa2O4 particles, produced in steps of mixing/milling the ingredients in H2O following thermal treating under 1200 degrees C. We compare spinel and partially inverse spinel structure in ZnGa2O4 particles using Rietveld refinement. Crystal structure of ZnGa2O4 particles was identified with two structural phases; normal spinel structure and partially inverse spinel structure using Rietveld refinement. It is found that the partially inverse spinel structures occupy nearly 13% and the rest is normal spinel structure. The obtained X-ray diffraction data show that lattice constant and the position of Oxygen atoms remain almost constant in both structures. The characterization of the particles was also improved using X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy measurements. The optical analyses were done with UV-visible spectroscopy. The band gap, calculated from climate point of UV-visible data, was found as 4.6 +/- 0.1 eV. Despite no unexpected compound (such as ZnO and Ga2O3) in the structure, the optical analyses were shown defective ZnO structure in ZnGa2O4. (C) 2012 Elsevier B.V. All rights reserved

Synthesis and characterization of ZnGa2O4 particles prepared by solid state reaction

We employed solid state reaction technique to synthesize ZnGa2O4 particles, produced in steps of mixing/milling the ingredients in H2O following thermal treating under 1200 degrees C. We compare spinel and partially inverse spinel structure in ZnGa2O4 particles using Rietveld refinement. Crystal structure of ZnGa2O4 particles was identified with two structural phases; normal spinel structure and partially inverse spinel structure using Rietveld refinement. It is found that the partially inverse spinel structures occupy nearly 13% and the rest is normal spinel structure. The obtained X-ray diffraction data show that lattice constant and the position of Oxygen atoms remain almost constant in both structures. The characterization of the particles was also improved using X-ray photoelectron spectroscopy and Fourier transforms infrared spectroscopy measurements. The optical analyses were done with UV-visible spectroscopy. The band gap, calculated from climate point of UV-visible data, was found as 4.6 +/- 0.1 eV. Despite no unexpected compound (such as ZnO and Ga2O3) in the structure, the optical analyses were shown defective ZnO structure in ZnGa2O4

Solution processing of morphotropic phase boundary BiFeO3-PbTiO3 thin films with reduced conductivity for high room temperature switchable polarization

[EN] The (1 – x)BiFeO-xPbTiO (BFO-PTO) perovskite solid solution has great potential for being used in practical devices, as it exhibits significant ferroelectric response at its morphotropic phase boundary (MPB). However, the significant conduction, particularly high electrical leakage currents that BFO-PTO films show at room temperature, deteriorates their functionality. This is mainly associated with the presence of multivalent iron along with A-site and oxygen vacancies. Here, solution-derived BFO-PTO thin films have been crystallized at low temperature on Pt/TiO/SiO/Si substrates, by a rapid thermal annealing process to minimize Bi and Pb volatilization. X-ray analyses have revealed that textured films are obtained with a pseudocubic perovskite structure and without the formation of detectable second phases. Microstructural studies indicated a columnar growth of the films with grain size well above the nanometric range, which, therefore, should not produce an appreciable reduction of the ferroelectric response due to size effects. Because of the relatively low content of charged defects produced in these BFO-PTO films during processing, ferroelectric hysteresis loops can be measured at room temperature. The highest value of remnant polarizations (2P= 58 μC/cm) was obtained for the 0.65BiFeO-0.35PbTiO (65BFO-35PTO) films, which suggests that this film composition lies in the proximity of the MPB where the coexistence of a highly textured  tetragonal phase and a rhombohedral one seems to occur.Layiq Zia acknowledges the Higher Education Commission of Pakistan (HEC) for financial support for his stay at ICMM-CSIC under the Indigenous 5000-PhD Fellowship Program (PIN: 112-27186-2PS1-143) and the International Research Support Initiative Program (IRSIP) (PIN: IRSIP 43 PSc 48). Ricardo Jiménez, Iñigo Bretos, Harvey Amorín, Miguel Algueró, and M. Lourdes Calzada acknowledge the financial support of the Spanish Projects PID2019-104732RB-I00, MAT2017-88788-R, and MAT2017-91772-EXP. Iñigo Bretos acknowledges financial support from the Ramón & Cajal Spanish Program. GHJ acknowledges financial support from the Pakistan Higher Education Commission (HEC, NRPU project number 8342). Enrique Rodríguez-Castellón thanks project RTI2018-099668-BC22 of Ministerio de Ciencia, Innovación y Universidades, and FEDER funds

Effect of A and B-site substitution with Pb, La and Ti on phase stabilization and multiferroic properties of BiFeO3

Abstract The work presents a comparative study of the effects of divalent (Pb), trivalent (La) and tetravalent (Ti) substituents on the multiferroic properties of BiFeO3 (BFO). Both A and B-sites were substituted to obtain the compositions i.e. (Bi1−x−yLaxPby)(Fe1−zTiz)O3 (x, y = 0, 0.1, 0.2 and z = 0, 0.05, 0.1, 0.15). Each of the substituent was particularly chosen i.e. Pb was chosen to keep the lone pair character which is the similar case as Bi ion. Additionally isovalent La was chosen to achieve single phase by reducing Bi volatization. Both these ions, on substitution, stabilized the crystal structure and suppressed the formation of extra phases which are unavoidable in pure BFO. All the Ti substituted and Bi0.8La0.2FeO3 compositions exhibited rhombohedral perovskite (R3c) phase, while Bi0.8Pb0.2FeO3 and Bi0.8La0.1Pb0.1FeO3 exhibited cubic phase. Mössbauer measurements revealed that impurity phase in case of compositions with divalent and trivalent substituents, disappeared completely when Ti substituted Fe. For all the compositions Fe ions were found in +3 state. High temperature dielectric properties showed that all the compositions were ferroelectric with paraelectric transition lying well above the room temperature. Weak ferromagnetism was found in Ti substituted compositions where coercivity was found to increase as the Ti concentration increases. All the BFO samples substituted with Pb, exhibited a dielectric anomaly in the temperature range, 100 °C ⩽ T ⩽ 250 °C. A systematic reduction in the intensity of the dielectric anomaly peak was observed as a function of Ti concentration which indicates that the anomaly is related to the conductivity and is element specific. However, Mössbauer data revealed absence of Fe2+ state, which ensured that it was not related with the presence of Fe2+ ions. Saturation polarization was found to increase as Ti concentration increased from 0% to 10%

Bulk-like ferroelectricity and magnetoelectric response of low-temperature solution-processed BiFeO3–PbTiO3 films on Ni for metallic MEMS

Simple and cost-effective procedures for the direct integration of ferroelectric perovskite oxides into Ni structures are necessary to realize related multifunctional metallic microelectromechanical systems, such as dual-source energy harvesters. This is especially difficult in the case of lead-containing morphotropic phase boundary materials for high piezoelectric response because the two components are thermodynamically incompatible and the formation of NiOx or perovskite oxide reduction takes place depending on the processing conditions. We show here that low-temperature solution processing is an effective means to kinetically limit nickel oxidation, capable of providing BiFeO3–PbTiO3 films on Ni plates at only 500 °C. Bulk-like ferroelectric properties and a distinctive magnetoelectric response were attained. This perovskite system, not explored before on Ni, has a much larger switchable polarization than the widely studied Pb(Zr,Ti)O3, and it is shown here to present an excellent downscaling behavior of ferroelectric properties until the verge of the nanoscale