Antiferromagnetically ordered state in spin tetramer system SeCuO3

U ovom radu proučavana su svojstva antiferomagnetski uređenog stanja u sustavu spinskih tetramera SeCuO3. Antiferomagnetski upredeno stanje nastaje ispod Néelove temperature TN = 8 K, a proučavano je metodom mjerenja magnetskog momenta sile u magnetskim poljima H ≤ 4:5 T pri temperaturama nižim od Néelove. Magnetski moment sile osjetljiv je na magnetsku anizotropiju čitavog uzorka, te mjerenjima kutne ovisnosti moguće je odrediti simetriju uređenog stanja za jednostavnije oblike dugodosežnog magnetskog uređenja. Koristeći elemente simetrije pripadne kristalne strukture konstruirali smo oblik magnetokristalne energije te ga iskoristili u fenomenološkom pristupu za opis magnetske anizotropije i spinskih reorijentacija u konačnom magnetskom polju u SeCuO3. Pri tome smo pretpostavili da je uređenje jednostavno jednoosno antiferomagnetsko kako je predloženo u literaturi. Dobiveni rezultati simulacija dobro se slažu s eksperimentom no postoje neka odstupanja koja ukazuju na kompliciranije magnetsko uređenje te pozivaju na daljnja istraživanja magnetske strukture ovog sustava.In this master thesis we studied properties of antiferromagnetically ordered state of spin tetramer system SeCuO3. This system orders antiferromagnetically below Néel temperature. We studied this state using torque magnetometry in magnetic fields H ≤ 4:5 T at temperatures lower than TN. Magnetic torque is sensitive to magnetic anisotropy of the sample, and by measuring angular dependence one can determine the symmetry of the magnetically ordered state for some simple long-range order. Applying symmetry elements of the crystal structure we construct magnetocrystalline energy which we use in phenomenological approach to describe magnetic anisotropy and spin reorientations in finite magnetic field in SeCuO3. In this approach simple uniaxial antiferromagnetic order as suggested in literature. Simulation results are in good agreement with experiment, however there are some discrepancies which to more complicated magnetic order and call for further investigation of magnetic structure of this system

Antiferromagnetically ordered state in spin tetramer system SeCuO3

U ovom radu proučavana su svojstva antiferomagnetski uređenog stanja u sustavu spinskih tetramera SeCuO3. Antiferomagnetski upredeno stanje nastaje ispod Néelove temperature TN = 8 K, a proučavano je metodom mjerenja magnetskog momenta sile u magnetskim poljima H ≤ 4:5 T pri temperaturama nižim od Néelove. Magnetski moment sile osjetljiv je na magnetsku anizotropiju čitavog uzorka, te mjerenjima kutne ovisnosti moguće je odrediti simetriju uređenog stanja za jednostavnije oblike dugodosežnog magnetskog uređenja. Koristeći elemente simetrije pripadne kristalne strukture konstruirali smo oblik magnetokristalne energije te ga iskoristili u fenomenološkom pristupu za opis magnetske anizotropije i spinskih reorijentacija u konačnom magnetskom polju u SeCuO3. Pri tome smo pretpostavili da je uređenje jednostavno jednoosno antiferomagnetsko kako je predloženo u literaturi. Dobiveni rezultati simulacija dobro se slažu s eksperimentom no postoje neka odstupanja koja ukazuju na kompliciranije magnetsko uređenje te pozivaju na daljnja istraživanja magnetske strukture ovog sustava.In this master thesis we studied properties of antiferromagnetically ordered state of spin tetramer system SeCuO3. This system orders antiferromagnetically below Néel temperature. We studied this state using torque magnetometry in magnetic fields H ≤ 4:5 T at temperatures lower than TN. Magnetic torque is sensitive to magnetic anisotropy of the sample, and by measuring angular dependence one can determine the symmetry of the magnetically ordered state for some simple long-range order. Applying symmetry elements of the crystal structure we construct magnetocrystalline energy which we use in phenomenological approach to describe magnetic anisotropy and spin reorientations in finite magnetic field in SeCuO3. In this approach simple uniaxial antiferromagnetic order as suggested in literature. Simulation results are in good agreement with experiment, however there are some discrepancies which to more complicated magnetic order and call for further investigation of magnetic structure of this system

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

The defect structure and electrical properties of the spark plasma sintered antimony-doped barium stannate

Barium stannate, BaSnO3 (BSO), is a perovskite-type alkaline earth metal stannate with almost ideal cubic structure. Appropriate doping can alter this wide band gap material’s electrical characteristics and change it either into a proton conductor or n-type semiconductor. In the case of Sb doping on Sn site, BSO becomes n-type semiconductor with high electrical conductivity at 25 °C. The major drawback of BSO-based ceramics is its low density. The conventional solid state procedure requires long thermal treatments with several intermittent grinding and heating steps at temperatures up to 1600 °C [1]. To overcome this problem, we used Spark Plasma Sintering technique (SPS) for the preparation of BaSn1-xSbxO3, (x = 0.00 (BSSO0) and 0.08 (BSSO8)) ceramic samples. The samples structural properties were investigated using XRD (X-Ray Powder Diffraction), XPS (X-Ray Photoelectron Spectrophotmetry) and SIMS (Secondary Ion Mass Spectrometry) analyses. XPS analysis revealed the existence of many structural defects, including mixed oxidation states of tin (Sn2+/Sn4+) and oxygen vacancies (VO) in both BSSO samples. The electrical properties of the BSSO ceramic samples were investigated in the temperature range of 4–300 K. The presence of oxygen vacancies in the BSSO0 sample led to the absence of the standard activated semiconductor behavior, showing almost linear temperature-dependent resistivity in the examined temperature range. On the other hand, the BSSO8 sample showed almost temperature-independent resistivity in the range of 70–300 K. This could be a consequence of the presence of many structural defects such as mixed oxidation states of Sn2+/Sn4+, probably Sb3+/Sb5+ and significant amount of O- species, as well as the presence of the low angle grain boundaries found in this sample. The BSSO8 ceramic sample could satisfy the huge demand for the linear resistors with moderate and high conductivity, due to its low and almost constant electrical resistivity in the wide temperature. 1. A.-M. Azad, L.L.W. Shyan, T.Y. Pang, C.H. Nee, Ceram. Int., 26 (2000) 685

Correlation between the microstructure and electrical properties of Sb-doped BaSnO3 ceramics

The non-magnetic, non-inductive electroconductive materials with linear current-voltage characteristic and low and almost constant electrical resistivity in the wide temperature range could be used in conditions unfavorable for metals and alloys. Particular emphasis is placed on the performance and endurance of these materials in conditions at constant high voltage, current, and energy, as well as operating in acidic and humid environmental conditions. The aim of this work was to investigate the influence of antimony concentration and sintering parameters on the structure, microstructure, and electrical properties of antimony-doped barium stannate, BaSn1-xSbxO3 (BSSO, x = 0,00; 0,04; 0,06; 0,08 and 0,10) to obtain conductive electroceramic samples with linear current-voltage (I- U) characteristics and low electrical resistivity. For this purpose three different sintering techniques were used: conventional, spark plasma and cold sintering. According to the X-ray diffraction (XRD) analysis, single-phase ceramic mater- ials with cubic BaSnO3 structure were obtained by conventional sintering at 1600 °C for 3 h and spark plasma sintering at 1100 °C for 5 min. Raising the spark plasma sintering temperature to 1200 °C induced the formation of Ba-rich secondary phase, Ba2SnO4. XRD analysis confirmed the presence of unreacted SnO2 and BaCO3 in cold sintered BaSn0.92Sb0.08O3 sample (310 °C for 5 min, 20 wt.% 1 M acetic acid). Scanning electron microscopy (SEM) indicates a significant decrease in grain size upon doping, regardless of the sintering technique. High-resolution transmission electron microscopy (HRTEM) revealed the presence of low angle grain boundaries (LAGBs) in conventionally and spark plasma sintered (1200 °C for 5 min) samples with x = 0.08. The results of electrical measurements confirmed the semiconducting properties of all BSSO, except the spark plasma sintered BaSn0.92Sb0.08O3 (1200 °C for 5 min) sample. This sample showed linear current-voltage characteristic, the lowest and almost constant electrical resistivity in the temperature range of 25–150 °C resulting from the loss of potential barriers at grain boundaries due to the large fraction of LAGBs present in BaSn0.92Sb0.08O3 ceramic sample

The structural, electrical and optical properties of spark plasma sintered BaSn1-xSbxO3 ceramics

Antimony doped barium-stannate dense ceramic materials were synthesized using spark plasma sintering technique out of mechanically activated precursor powders. The influence of various Sb concentrations (x =0.00 – 0.10) on properties of BaSn1-xSbxO3 ceramics was investigated. Relative densities of prepared samples were in the range of (79–96) %. TEM analysis revealed the presence of many dislocations in undoped BaSnO3, and their significant reduction upon doping with Sb. All samples except BaSn0.92Sb0.08O3 exhibit non-linear I-U characteristic, typical for semiconductors with potential barrier at grain boundaries. Low angle grain boundaries found only in BaSn0.92Sb0.08O3 caused the loss of potential barrier at grain boundaries which was confirmed by AC impedance spectroscopy measurements. Consequently, BaSn0.92Sb0.08O3 showed the lowest electrical resistivity and linear I-U characteristic. UV–vis analysis confirmed the increasing of band gap (Burstein–Moss shift) values in all doped samples.This is the peer-reviewed version of the manuscript: Vukasinovic J, Pocuca-Nesic M, Golic DL, Ribic V, Brankovic Z, Savic SM, Dapcevic A, Bernik S, Podlogar M, Kocen M, Rapljenovic Z, Ivek T, Lazovic V, Dojcinovic B, Brankovic G, The structural, electrical and optical properties of spark plasma sintered BaSn1-xSbxO3 ceramics, Journal of the European Ceramic Society (2020), 40, 15, 5566-5575, doi: [https://doi.org/10.1016/j.jeurceramsoc.2020.06.062]The published version: [http://cer.ihtm.bg.ac.rs/handle/123456789/3628

Antiferromagnetically ordered state in spin tetramer system SeCuO3

U ovom radu proučavana su svojstva antiferomagnetski uređenog stanja u sustavu spinskih tetramera SeCuO3. Antiferomagnetski upredeno stanje nastaje ispod Néelove temperature TN = 8 K, a proučavano je metodom mjerenja magnetskog momenta sile u magnetskim poljima H ≤ 4:5 T pri temperaturama nižim od Néelove. Magnetski moment sile osjetljiv je na magnetsku anizotropiju čitavog uzorka, te mjerenjima kutne ovisnosti moguće je odrediti simetriju uređenog stanja za jednostavnije oblike dugodosežnog magnetskog uređenja. Koristeći elemente simetrije pripadne kristalne strukture konstruirali smo oblik magnetokristalne energije te ga iskoristili u fenomenološkom pristupu za opis magnetske anizotropije i spinskih reorijentacija u konačnom magnetskom polju u SeCuO3. Pri tome smo pretpostavili da je uređenje jednostavno jednoosno antiferomagnetsko kako je predloženo u literaturi. Dobiveni rezultati simulacija dobro se slažu s eksperimentom no postoje neka odstupanja koja ukazuju na kompliciranije magnetsko uređenje te pozivaju na daljnja istraživanja magnetske strukture ovog sustava.In this master thesis we studied properties of antiferromagnetically ordered state of spin tetramer system SeCuO3. This system orders antiferromagnetically below Néel temperature. We studied this state using torque magnetometry in magnetic fields H ≤ 4:5 T at temperatures lower than TN. Magnetic torque is sensitive to magnetic anisotropy of the sample, and by measuring angular dependence one can determine the symmetry of the magnetically ordered state for some simple long-range order. Applying symmetry elements of the crystal structure we construct magnetocrystalline energy which we use in phenomenological approach to describe magnetic anisotropy and spin reorientations in finite magnetic field in SeCuO3. In this approach simple uniaxial antiferromagnetic order as suggested in literature. Simulation results are in good agreement with experiment, however there are some discrepancies which to more complicated magnetic order and call for further investigation of magnetic structure of this system

Electrodynamics in Organic Dimer Insulators Close to Mott Critical Point

Organic layered charge-transfer salts κ -(BEDT-TTF) 2 X form highly frustrated lattices of molecular dimers in which strong correlations give rise to Mott insulating states situated close to the metal-to-insulator phase boundary. The salts κ -(BEDT-TTF) 2 Cu 2 (CN) 3 and κ -(BEDT-TTF) 2 Ag 2 (CN) 3 have been considered as prime candidates for a quantum spin liquid, while κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl has been suggested as a prototypical charge-order-driven antiferromagnet. In this paper, we summarize and discuss several key results, including some not reported previously, obtained in search to clarify the competition of these two ground states. The origin of anomalous dielectric response found at low temperatures in all three salts is also discussed. We conclude by pointing out the relevant new insights into the role of frustration and random disorder in the suppression of magnetic ordering and formation of the spin liquid state