Uređenja naboja u jako koreliranim sustavima

At the focus of this thesis are systems with strong correlations and reduced dimensionality: the inorganic quasi-1D chain compound BaVS3 with itinerant and localized charges, spin chain and ladder composite (La,Y,Sr,Ca)14Cu24O41, and the quasi-2D organic conductor α-(BEDT-TTF)2I3 with the so-called horizontal stripe charge order. Samples have been characterized by transport and optical methods used in solid state and low-temperature physics: anisotropy of dc conductivity, nonlinear conductivity and low-frequency dielectric response as well as terahertz and infrared spectroscopy. In the orbitally ordered phase of BaVS3 evidence is presented of collective excitations below the Peierls-like metal-insulator transition. Further, in (La,Y)y(Sr,Ca)14-yCu24O41 a crossover in charge transport is demonstrated at y ≈ 2 from a one-dimensional hopping along the chain subsystem to a quasi-two-dimensional charge conduction in the ladder planes. It is found that an interdependent formation of long-range orders takes place in the two subsystems: an antiferromagnetic dimer order in chains and a charge-density wave in ladders. Lastly, electrodynamic response in the organic conductor α-(BEDT-TTF)2I3 has been investigated. Optical spectra show a sudden appearance of long-range charge order below the phase transition. Rather than a fully localized Wigner crystal, our results favor an interesting interpretation of horizontal stripes as a cooperative bond-charge density wave with a ferroelectric-like nature.U fokusu ove doktorske disertacije nalaze se sustavi s jakim elektronskim korelacijama i reduciranom dimenzionalnošću: anorganski kvazi-1D lanačasti spoj BaVS3 s itinerantnim i lokaliziranim nabojima, kompozit kupratnih lanaca i ljestvica (La,Y,Sr,Ca)14Cu24O41, te kvazi-2D organski vodič α-(BEDT-TTF)2I3 koji pokazuje tzv. uređenje naboja s horizontalnim prugama. Uzorci su karakterizirani optičkim metodama i mjerenjem električnog transporta: anizotropija istosmjerne vodljivosti, niskofrekventni dielektrični odziv te terahertzna i infracrvena spektroskopija. U fazi orbitalnog uređenja BaVS3 nađeni su dokazi kolektivnih pobuđenja ispod faznog prijelaza iz metala u izolator sličnog Peierlsovom. Nadalje, u (La,Y)y(Sr,Ca)14-yCu24O41 je na y ≈ 2 pokazano postupno prebacivanje transporta naboja s jednodimenzionalnog preskakivanja duž lanaca na kvazi-dvodimenzionalno vođenje u ravninama ljestvica. Rezultati ukazuju na zanimljivu međuzavisnost stvaranja dugodosežnog uređenja u dva sustava: antiferomagnetskog dimerskog uređenja na lancima, te vala gustoće naboja na ljestvicama. Na kraju, ispitan je i elektrodinamički odziv α-(BEDT-TTF)2I3. U optičkim spektrima pronalazimo dokaze naglog dugodosežnog uređenja naboja. Kao najkonzistentniju sliku te uređene faze predlažemo zanimljiv pogled horizontalnih pruga kao kooperativnog vala gustoće veza i naboja feroelektrične prirode umjesto potpuno lokaliziranog Wignerovog kristala

Methemoglobinemija - prikaz slučaja i pregled literature

The objective of this case report is to present a patient with acquired methemoglobinemia due to poisoning of an unknown cause. A 55-year-old man was brought to the Emergency Department, University Hospital Center Zagreb, with an unwell appearance, cyanotic, restless, and presented with a quantitative consciousness disorder. An initial assessment showed decreased oxygen saturation (SpO2 85 [%]), while point-of-care arterial blood gas (ABG) analysis assessed normal partial pressure of oxygen (pO2). Severe lactic acidosis with a compensatory drop in partial pressure of carbon dioxide (pCO2) and high rates of methemoglobin were found. Supportive oxygen therapy and crystalloid solutions were administered, which resulted in rapid clinical recovery within 40 minutes of the initial assessment. Clinical recovery was accompanied by normalized ABG test results taken serially. Typical antidotes, methylene blue and vitamin C, were not administered due to rapid clinical improvement. Methemoglobinemia can be congenital (hereditary) or acquired (toxic). Both conditions are rarely seen in emergency departments, nevertheless, they should be approached properly since methemoglobinemia can be a severe, and fatal, condition. Methemoglobinemia symptoms are the results of inadequate oxygen transport. The diagnosis was confirmed by co-oximetry, while three clinical entities suspected methemoglobinemia: refractory hypoxia, “cyanosis-saturation gap“ and dark brown blood. This paper reports our patient’s clinical presentation, discusses the causes and mechanisms of possible poisoning, and reviews recent guidelines for methemoglobinemia management.Svrha ovog rada je prikaz slučaja pacijenta sa stečenom methemoglobinemijom uslijed trovanja nepoznatog uzroka. 55-godišnji muškarac zapuštenog izgleda dovežen je u Objedinjeni hitni bolnički prijem (OHBP ) Kliničkog bolničkog centra (KBC) Zagreb cijanotičan, nemiran i kvalitativno promijenjenog stanja svijesti. U inicijalnoj obradi nađena je snižena saturacija kisikom (SaO2 85[%]), dok je plinska analiza arterijske krvi ukazivala na zadovoljavajuće vrijednosti parcijalnog tlaka kisika. Nađena je teška laktacidoza s kompenzatorno sniženim parcijalnim tlakom ugljikovog dioksida, a zamijećen je i visok postotak methemoglobina. Na primijenjenu suportivnu oksigenoterapiju te terapiju kristaloidnim otopinama, pacijentovo se kliničko stanje rapidno oporavlja unutar četrdesetak minuta, što se prati i normalizacijom serijski evaluiranog acidobaznog statusa. S obzirom na povoljan klinički tijek, nije bilo potrebe za primjenom antidota – metilenskog modrila i vitamina C. Postoje urođena (genetska) i stečena (toksična) methemoglobinemija. Oba stanja se rijetko viđaju na hitnom prijemu, a stečena methemoglobinemija može biti životno ugrožavajuće stanje. Simptomi methemoglobinemije izravna su posljedica neadekvatnog transporta kisika. Dijagnoza se postavlja na temelju ko-oksimetrije, ali sama klinička sumnja može se postaviti na temelju sljedeća tri entiteta: refraktorne hipoksije, „cyanosis-saturation gap“ i smeđe boje krvi. U ovom radu osvrnut ćemo se na klinički tijek našeg pacijenta, dotaći se potencijalnih mehanizama trovanja i uzroka toksične methemoglobinemije te prikazati recentne preporuke za zbrinjavanje ovakvih slučaja

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

Elementary excitation in the spin-stripe phase in quantum chains

Elementary excitations in condensed matter capture the complex many-body dynamics of interacting basic entities in a simple quasiparticle picture. In magnetic systems the most established quasiparticles are magnons, collective excitations that reside in ordered spin structures, and spinons, their fractional counterparts that emerge in disordered, yet correlated spin states. Here we report on the discovery of elementary excitation inherent to spin-stripe order that represents a bound state of two phason quasiparticles, resulting in a wiggling-like motion of the magnetic moments. We observe these excitations, which we dub “wigglons”, in the frustrated zigzag spin-1/2 chain compound β-TeVO4, where they give rise to unusual low-frequency spin dynamics in the spin-stripe phase. This result provides insights into the stripe physics of strongly-correlated electron systems

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