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Variable range hopping transport and dielectric relaxation mechanism in GdCrO3 rare-earth orthochromite perovskite

Journal of Rare Earths 2024年第7期42卷 1304-1316页

作者： Muhammad Javed Ayaz Arif Khan Jamal Kazmi Naeem Akbar Said Nasir Khisro Amanullah Dar Aleem Dad Khan Tareen Mohd Ambri Mohamed Department of Physics The University of Azad Jammu and Kashmir Department of Physics University of Kotli Azad Jammu and Kashmir Institute of Microengineering and Nanoelectronics Universiti Kebangsaan Malaysia Department of Mathematics University of Kotli Azad Jammu and Kashmir

The polycrystalline GdCrO3（GCO） perovskite orthochromite was synthesized by the sol-gel autocombustion method.The Rietveld refined X-ray diffraction（XRD） profile of GCO confirms that the orthorhombic phase crystallizes in perovskite crystal structure with space group Pbnm.The transmission electron microscopy and selected area electron diffraction divulge the polycrystalline nature of the perovskite chromite.The field emission scanning electron microscopy（FESEM） images reveal the micro structural polyhedral growth of grains separated by sharp grain boundaries.The chemical states of the ions present in the compound were investigated by X-ray photoelectron spectroscopy（XPS） studies,and the electrical pathways were identified.Complex impedance studies were carried out in the experimental frequency and temperature ranges of 40 Hz-4 MHz and 178-408 K,respectively.The equivalent circuit model（RGQG）(RGBQGB) resolves the impedance response into two contributions originating from the intra-grain and inter-granular micro-constituents of the material.The electrical conduction mechanism is based on the Mott variable range hopping model.The complex electric modulus studies demonstrate the short-and long-range mobility of the charge carriers and rule out the presence of electrode effects on the dielectric relaxation mechanism of the material.The decreasing pattern of dielectric permittivity with frequency is explained by the Maxwell-Wagner type of polarization.The frequency dependence of the loss factor exhibits the presence of thermally activated relaxation time distribution in the material.

关键词： auto-combustion Dielectric Electrical transport Electro-ceramic Impedance Perovskite

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Structural, optical and electron paramagnetic resonance studies on Cu-doped ZnO nanoparticles synthesized using a novel auto-combustion method

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Frontiers of Materials Science 2013年第2期7卷 196-201页

作者： R. ELILARASSI G. CHANDRASEKARAN Magnetism and Nanomagnetic Materials Lab Department of Physics School of Physical Chemical and Applied Sciences Pondicherry University Puducherry 605014 India

Nanocrystalline Zn1_xCuxO （x = 0, 0.02, 0.04, 0.06, 0.08） samples were synthesized by a novel auto-combustion method using glycine as the fuel material. The structural, optical and magnetic properties of the samples were characterized using XRD, SEM, photoluminescence （PL） and electron paramagnetic resonance （EPR） spectro- scopies. The XRD spectra of samples reveal the hexagonal wurtzite structures of ZnO. As the copper content increases, a diffraction peak at 28 = 39° corresponding to secondary phase of CuO （[111] crystalline face） appears when x≤ 6 mol.%. PL spectra of the samples show a strong ultraviolet （UV） emission and defect related visible emissions. Cu-doping in ZnO can effectively adjust the energy level in ZnO, which leads to red shift in the emission peak position in UV region. The EPR spectra of Cu-doped ZnO nanoparticles show a distinct and broad signal at room temperature, suggesting that it may be attributed to the exchange interactions within Cu2＋ ions.

关键词： Cu-doped ZnO auto-combustion luminescence electron paramagneticresonance （EPR）

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Enhanced room temperature ferromagnetism in Cr-doped ZnO nanoparticles prepared by auto-combustion method

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Journal of Semiconductors 2018年第4期39卷 20-27页

作者： Khizar-ul Haq M.Irfan Muhammad Masood Murtaza Saleem Tahir Iqbal Ishaq Ahmad M.A.Khan M.Zaffar Muhammad Irfan Department of Physics Mirpur University of Science and Technology (MUST) Department of Physics SBASST Lahore University of Management Sciences Experimental Physics Labs National Centre for Physics Quaid-e-Azam University Department of Physics University of Azad Jammu and Kashmir Muzaffarabad

Zn1-xCrxO （x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.09） nanoparticles were synthesized, by an auto-com- bustion method. Structural, optical, and magnetic characteristics of Cr-doped ZnO samples calcined at 600 ℃ have been analyzed by using X-ray diffraction （XRD）, field emission scanning electron microscope （FESEM）, UV-Vis spectroscopy and vibrating sample magnetometer （VSM）. The XRD data confirmed the hexagonal wurtzite structure of pure and Cr-doped ZnO nanoparticles. The calculated values of grain size using Scherrer＇s formula are in the range of 30.7-9.2 nm. The morphology of nanopowders has been observed by FESEM, and EDS results con- firmed a systematic increase of Cr content in the samples and clearly indicate with no impurity element. The band gaps, computed by UV-Vis spectroscopy, are in the range of 2.83-2.35 eV for different doping concentrations. By analyzing VSM data, significantly enhanced room temperature ferromagnetism is identified in Cr-doped ZnO samples. The value of magnetization is a 12 times increased of the value reported by Daun et al. （2010）. Room temperature ferromagnetism of the nanoparticles is of vital prominence for spintronics applications.

关键词： Cr-doped ZnO auto-combustion DMS ferromagnetism

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Morphology and magnetic traits of strontium nanohexaferrites:Effects of manganese/yttrium co-substitution

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Journal of Rare Earths 2019年第7期37卷 732-740页

作者： M.A.Almessiere Y.Slimani H.S.El Sayed A.Baykal Department of Physics College of ScienceImam Abdulrahman Bin Faisal UniversityP.O.Box 198231441 DammamSaudi Arabia Department of Nano-Medicine Research Institute for Research&Medical Consultations(IRMC)Imam Abdulrahman Bin Faisal UniversityP.O.Box 198231441 DammamSaudi Arabia Department of Biophysics Institute for Research&Medical Consultations(IRMC)Imam Abdulrahman Bin Faisal UniversityP.O.Box 198231441 DammamSaudi Arabia

Doped strontium(Sr) hexaferrites appeared potential candidates for microwave absorber applications.Driven by this idea, we examined the influence of manganese(Mn) and yttrium(Y) co-substitution on the microstructures,morphology and magnetic properties of Sr nanohexaferrites(Sr1-xMnxFe12-yYyO19,where 0.0 ≤ x = y ≤ 0.5) synthesized via citrate sol-gel auto-combustion technique. As-prepared samples were thoroughly characterized using diverse analytical tools. X-ray diffraction pattern reveals a single Mhexagonal crystalline phase. FE-SEM, TEM, HR-TEM show a hexagonal platelet-like structure. The magnetic hysteresis loops(measured at room and low temperature) of the as-prepared nanohexaferrites exhibit ferromagnetic(FM) behavior. Magnetic parameters including the saturation magnetization,remanence, coercive and magneto-crystalline anisotropy field are found to decrease with the increase in Mn2+ and Y3+ contents. Zero-and normal-field cooled magnetization measurements in the range of 2-400 K display the complete absence of blocking temperature, confirming the characteristic ferromagnetic behavior of the proposed composition.

关键词： Strontium hexaferrite Sol-gel auto-combustion Microstructure Morphology Magnetic properties Rare earths

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Shape control of CeO2 nano-particles and synthesis of nano-metric solid acid SO42-/CeO2

Shape control of CeO2 nano-particles and synthesis of nano-m...

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第十届全国稀土元素分析化学学术报告会

作者： Jingzhang Gao*, Youli Qi, Wu Yang, Xiaojun Guo, Shengyin Li, Xien Li Chemistry and Chemical Engineering College, Northwest Normal University, Lanzhou 730070, PR China Rcccivcd 15 January 2003 rcccivcd in rcviscd form 18 May 2003 acccptcd 28 May 2003

Nano-particles of CeO2 with the smallest average particle size (18.7 nm) and spherical morphology were obtained from a mixture solution of Ce(NO3)3-6H2O, citric acid, polyvinyl alcohol by an auto-combustion process exploiting sol-gel as precursors. The course of size control and shape control by polyvinyl alcohol was examined in detail. A transmission electron microscopy (TEM) and an atomic force microscopy (AFM) were employed to characterize the particle-size and morphology of CeO2 particles. In addition, a sort of nano-metric solid acid SO42-/CeO2 based on CeO2 nano-particles was prepared by macerating, filtering, drying and calcining processes. The particle-size of SO42-/CeO2 was also assessed by TEM. The composition of SO42-/CeO2 was analyzed by X-ray diffraction (XRD) and infrared spectra (IR). The influencing factors in the formation of SO42-/CeO2 were examined in the reaction of isobutyl alcohol and acetic acid. The relationship between the catalytic activity and the adsorption amount of SO42- groups was examined by precipitation titration. (?) 2003 Elsevier B.V. All rights reserved.

关键词： auto-combustion Sol-gel Shapc control Siz: control and solid acid

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