Na spor. nasl. str.:Chemical and mechanochemical syntheses of yttrium manganite based multiferroics.

U okviru ove doktorske disertacije ispitivan je uticaj parametara mehanohemijske i hemijske sinteze na strukturu i svojstva prahova i keramičkih uzoraka itrijum- -manganita (YMnO3, YMO).Smeša prahova Y2O3 i Mn2O3 mlevena je u planetarnom mlinu tokom vremenskih perioda od 60 – 720 min. Rendgenska analiza dobijenih prahova pokazala je da su tokom mlevenja od 240, 360 i 720 min dobijeni jednofazni pahovi rombičnog YMnO3 (o-YMO). Primarne čestice u prahovima su ispod 100 nm, a produžavanje vremena mlevenja dovodi do aglomeracije. Magnetna svojstva ukazuju da su prahovi u osnovi antiferomagnetični, uz delimično narušeno uređenje spinova prisustvom Mn4+-jona...Within this doctoral dissertation, the influence of mechanochemical and chemical synthesis parameters on the structure and properties of yttrium manganite (YMnO3, YMO) powders and ceramics was investigated. Mixture of Y2O3 and Mn2O3 was milled in a planetary ball mill for periods of 60 – 720 min. X-ray analysis of the resulting powders showed that single-phased orthorhombic YMnO3 (o-YMO) powders were obtained for milling periods of 240, 360 and 720 min. The size of primary particles in the powders was below 100 nm, while a prolongation of the milling time led to agglomeration. The magnetic properties indicated that the powders were basically antiferromagnetic with partially disordered spins by the presence of Mn4+ ions..

Chemical and mechanochemical syntheses of yttrium manganite based multiferroics.

U okviru ove doktorske disertacije ispitivan je uticaj parametara mehanohemijske i hemijske sinteze na strukturu i svojstva prahova i keramičkih uzoraka itrijum- -manganita (YMnO3, YMO). Smeša prahova Y2O3 i Mn2O3 mlevena je u planetarnom mlinu tokom vremenskih perioda od 60 – 720 min. Rendgenska analiza dobijenih prahova pokazala je da su tokom mlevenja od 240, 360 i 720 min dobijeni jednofazni pahovi rombičnog YMnO3 (o-YMO). Primarne čestice u prahovima su ispod 100 nm, a produžavanje vremena mlevenja dovodi do aglomeracije. Magnetna svojstva ukazuju da su prahovi u osnovi antiferomagnetični, uz delimično narušeno uređenje spinova prisustvom Mn4+-jona...Within this doctoral dissertation, the influence of mechanochemical and chemical synthesis parameters on the structure and properties of yttrium manganite (YMnO3, YMO) powders and ceramics was investigated. Mixture of Y2O3 and Mn2O3 was milled in a planetary ball mill for periods of 60 – 720 min. X-ray analysis of the resulting powders showed that single-phased orthorhombic YMnO3 (o-YMO) powders were obtained for milling periods of 240, 360 and 720 min. The size of primary particles in the powders was below 100 nm, while a prolongation of the milling time led to agglomeration. The magnetic properties indicated that the powders were basically antiferromagnetic with partially disordered spins by the presence of Mn4+ ions..

Chemical and mechanochemical syntheses of yttrium manganite based multiferroics.

U okviru ove doktorske disertacije ispitivan je uticaj parametara mehanohemijske i hemijske sinteze na strukturu i svojstva prahova i keramičkih uzoraka itrijum- -manganita (YMnO3, YMO). Smeša prahova Y2O3 i Mn2O3 mlevena je u planetarnom mlinu tokom vremenskih perioda od 60 – 720 min. Rendgenska analiza dobijenih prahova pokazala je da su tokom mlevenja od 240, 360 i 720 min dobijeni jednofazni pahovi rombičnog YMnO3 (o-YMO). Primarne čestice u prahovima su ispod 100 nm, a produžavanje vremena mlevenja dovodi do aglomeracije. Magnetna svojstva ukazuju da su prahovi u osnovi antiferomagnetični, uz delimično narušeno uređenje spinova prisustvom Mn4+-jona...Within this doctoral dissertation, the influence of mechanochemical and chemical synthesis parameters on the structure and properties of yttrium manganite (YMnO3, YMO) powders and ceramics was investigated. Mixture of Y2O3 and Mn2O3 was milled in a planetary ball mill for periods of 60 – 720 min. X-ray analysis of the resulting powders showed that single-phased orthorhombic YMnO3 (o-YMO) powders were obtained for milling periods of 240, 360 and 720 min. The size of primary particles in the powders was below 100 nm, while a prolongation of the milling time led to agglomeration. The magnetic properties indicated that the powders were basically antiferromagnetic with partially disordered spins by the presence of Mn4+ ions..

Synthesis, characterization and photocatalytic properties of LaNiO3-based powders

Lanthanum nickelate (LaNiO3, LNO) belongs to the group of materials with perovskite-type structure and it crystallizes in rhombohedrally distorted perovskite lattice. This material exhibits interesting electrical, magnetic, optical and catalytic properties and it is suitable for various applications. Still, the preparation of single phase LNO is difficult, because at temperatures above 850 °C it decomposes into the lower oxides with formula Lan+1NinO3n+1 (n = 3, 2, 1) and NiO. In this work we present the synthesis of pure and Nb doped LNO powders, LaNi1-xNbxO3 (x = 0.000, 0.005, 0.010) prepared from mechanochemically activated oxide precursors – La2O3, NiO and Nb2O5. For this experiment, precursor powders homogenized in isopropyl alcohol were dried and mechanochemically activated in the planetary ball mill for 3 h. As-prepared powders were calcined at 700 °C for 3 h in air and further analyzed by X-ray diffraction analysis (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and UV-Vis spectroscopy. Photocatalytic activity in visible light was investigated. The XRD analysis of undoped LNO revealed the existence of rhombohedral LaNiO3 and small amount of NiO phase. The doped samples, apart from LNO, contained products of thermal decomposition – layered oxides and NiO. TEM and HRTEM analyses of undoped LNO revealed the presence of agglomerated particles with single particle size being in the range of 20–40 nm. Doping with Nb led to decrease of agglomeration process and allowed better dispersion between particles of LNO based powders. Calculated band gaps were 1.12 eV, 0.89 eV and 0.87 eV for x = 0.00, 0.005, 0.010. The absorption spectra indicated photocatalytic degradation of Reactive Orange 16, textile dye used as a model in these experiments

The crucial role of defect structure in understanding the electrical properties of spark plasma sintered antimony doped barium stannate

The influence of structural defects in spark plasma sintered BaSn1-xSbxO3 (BSSO, x=0.00 and 0.08) ceramic samples on their electrical properties was investigated in the temperature range of 300–4K. X-ray photoelectron spectroscopy (XPS) revealed the presence of point defects, primarily oxygen vacancies (VO) and mixed oxidation states of tin (Sn2+/Sn4+) in both samples. As a result, the undoped BSSO sample exibited a non-standard semiconductor behavior, retaining its temperaturedependent resistivity. The electrical resistivity of the doped samples was two orders of magnitude lower than that of the undoped sample. The presence of structural defects such asVO, mixed oxidation states of the constituent elements, and significant amounts ofO− species make the electrical resistivity of the doped sample constant in the temperature range of 300–70 K, indicating heavily-doped semiconductor behavior

Hard Template Synthesis of Nanomaterials Based on Mesoporous Silica

Diverse hard template synthetic methodologies are being employed for the synthesis of mesostructured metal oxide and carbon nanomaterials, with the application of mesoporous silica as the hard template. We describe the main differences and advantages/disadvantages between the soft and hard templated synthetic routes, provide an overview of the synthesis and characteristics of different templating mesoporous silica nanomaterials and discuss on practical aspects of the hard template synthetic methodology for obtaining various metal-oxide and carbon-based mesostructured nanomaterials. Also, we cover various recent applications of thus constructed mesostructured metal oxide and carbon nanomaterials, such as sensing, energy storage, fuel cells, and catalysis, which demonstrate the highly promising character of the hard template methodology for the synthesis of a new generation of nanomaterials with broad application potential

Electrical properties of BaSn(1-x)SbxO3 ceramics materials

BaSnO3 is a perovskite oxide widely used as dielectric ceramic material, thermally stable capacitor in electronic industry and chemical humidity sensor. It is also an electrical insulator (band gap ~ 3.1 eV), which becomes an n-type conductor by doping. The aim of this work was to prepare BaSn(1−x)SbxO3 (BSSO) by mechanochemically assisted solid-state synthesis, starting from BaCO3, SnO2 and Sb2O3 as precursors. The concentration of Sb in BSSO was varied from 0.04 to 0.1. All starting mixtures were homogenized and activated in a planetary ball mill with isopropanol as a solvent. As-prepared powders were dried and calcined at 900 °C for 4 h. After calcination, powders were uniaxially pressed into pellets and sintered at temperature of 1200 °C for 3 h. Phase composition and microstructure of perovskite BSSO were identified by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The influence of Sb doping on electrical characteristics of ceramic material was determined by measuring the current-voltage characteristics for all samples at room temperature in air. The band gap values for BSSO calculated using Kubelka-Munk transformation and Tauc linearization of the obtained diffuse reflectance spectra, confirmed conductive behavior of preparedceramic samples

Synthesis and characterization of Nb-doped lanthanum nickelate La(Ni,Nb)O3

Perovskite type ceramic materials with general formula ABO3 are very important class of materials due to their various chemical and physical properties. They have wide applications such as electrode material for solid state fuel cells (SOFC), capacitors, resistors, superconductors, catalysts, electrolytes, microwave devices, and magnetoresitant materials [1, 2]. Lanthanum nickelate (LaNiO3, LNO) is a ternary oxide with rhombohedrally distorted perovskite lattice. In LNO trivalent nickel ions (Ni3+) are in low spin configuration (t2g 6eg 1) and the conduction band is formed by the hybridization of the egorbitals of Ni3+ and the p-orbitals of oxygen. As a result, LNO shows metallic n-type conductivity in wide temperature range [3]. For this reason LNO has been proposed as a cathode material for intermediate-temperature SOFCs (IT-SOFCs) with operating temperature range of 650-800 °C. The possible dawbacks of LNO as a potential material for this application are poor density and thermal unstability at temperatures higher than 850 °C, when LNO starts gradually to decompose into the lower oxides Lan+1NinO3n+1 (n = 3, 2, 1) and NiO. Still, all of these La-Ni-O compounds exhibit high electronic conduction within the NiO6 octahedra in their perovskite layers and excellent oxygen ionic conductivity through oxygen interstitials on the LaO rock-salt plane. Also, their coefficient of thermal expansion (CTE) matches those of materials commonly used as IT-SOFC electrolyte and anode [1]. A possible use of LNO as a cathode for SOFC requires the improvement of its thermal stability and enhancement of density of ceramic samples. The aim of this work was to fullfill these requirements by doping of lanthanum-nickelate into the B site. Using transition metal of higher valency than Ni3+ as a dopant, could enhance the electron concentration and carrier mobility, which results in improvement of electrical conductivity of ceramic material. Doping could also influence the sintering process and improve the density of the ceramic materials. In this work we present dense ceramic materials of LaNi1- xNbxO3 (x = 0.005, 0.05) prepared by mechanochemically assisted solid state method. La2O3, NiO and Nb2O5, used as a precursor reagents, were mechanochemically activated in the planetary ball mill for 5 h. Obtained powders were calcined at 700 °C for 3h in air, and afterwards sintered at 900 °C and 1200 °C for 2 h and 10 h in different atmospheres (air and oxygen). The influence of Nb doping on electrical properties and microstructure of LaNi1-xNbxO3 ceramic materials was investigated. All samples were analyzed by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Electrical conductivity of ceramic LaNi1-xNbxO3 samples was measured in different mediums and complete characterization of electrical properties was performed. The XRD analysis indicated the existence of secondary phases Lan+1NinO3n+1 and NiO along with the rhombohedral LaNiO3. Samples sintered at 900 °C in oxygen atmosphere for 2 h had density of 64 % and 60 % for x = 0.005 and x = 0.05 (Fig. 1). The electrical conductivity was improved by doping with Nb, and obtained values were 2.7 S cm and 2.6 S cm for x = 0.005 and x = 0.05 at room temperature. The obtained results confirmed that doping by Nb along with sintering in oxygen atmosphere can improve electrical conductivity, density, and thermal stability. References [1] R.K. Sharma, E. Djurado, J Mater Chem A, 5 (2017) 22277-22287. [2].A. S. Bhalla, R. Guo, R. Roy, Mat Res Innovat, 4 (2000) 3-26. [3] K. Sreedhar et al., Phys Rev B, 46 (1992) 6382-6386

COMPARISON OF SENSING PROPERTIES OF SnO2/KIT-5 AND SnO2 HUMIDITY SENSORS

In this work, two different syntheses approaches – nanocasting and sol-gel technique were employed for the preparation of SnO2 powders for humidity sensors. Stock solution of SnCl2 in ethanol (0.5 M) was used as a Sn-precursor for both syntheses. In the first procedure, this solution was infiltrated by wet impregnation method into the hydrothermally prepared KIT-5 used as silica template. Mesoporous SnO2/KIT-5 hybrid was obtained after two step loading/calcination process. Calcination was performed at 550 C for 5 h. In the second procedure, silica template was excluded from synthetic path. Ethanol solution of SnCl2 was slowly heated to form the gel which was later submitted to the same calcination conditions resulting in the preparation of SnO2 nanopowder. By dispersing the as prepared powders in the ethyl-cellulose/α-terpineol solution and adding a few drops of acetic acid in the mixture, viscous pastes were prepared and further homogenized for 24 h with magnetic stirrer. Using doctor blade applicator a few micron thick films were deposited onto alumina substrates provided with interdigitated Pt/Ag electrodes. Sensors’ characteristics were compared by measuring the change of the complex impedance of the samples exposed to a humid climate chamber environment at different temperatures and RH values from 40 % to 90 % at 25 °C and from 30 % to 90 % at 50 °C. The value of impedance measured at 42 Hz and within the RH range of 40 % to 90 %, changes 53 times at 25 °C, and 96 times at 50 °C. In contrast, for the sensor prepared from chemically derived SnO2, the impedance changes in a moderate way – 8 times at 25 °C and 3 times at 50 °C. Fast response/recovery time of the SnO2/KIT-5 hybrid sensor exposed to humidity change from 40 % – 90 % at room temperature, confirmed superior potentials of this material for humidity sensing over the SnO2

TEM and FESEM investigation of lanthanum nickelate thin films obtained by chemical solution deposition

Lanthanum nickelate (LNO) is a perovskite oxide material with metallic conductivity in a wide temperature range which makes it suitable for application as electrode material for thin films. In this paper LNO thin films were prepared by polymerizable complex method from the diluted citrate solutions. Precursor solutions were spin coated onto Si-substrates with amorphous layer of SiO2. Deposited layers were thermally treated from the substrate side with low heating rate (1°/min) up to 700°C and finally annealed for 10 hours. Results of AFM and FESEM showed that films are very smooth (Ra = 4 nm), dense, crack-free and with large square-shaped grains (170 nm). According to FESEM and TEM results the obtained four-layered film was only 65 nm thin. EBSD and XRD analyses confirmed polycrystalline microstructure of the films without preferential orientation. It was concluded that the presence of SiO2 layer on Si substrate prevents epitaxial or oriented growth of LNO