Submitted by Fabio Sobreira Campos da Costa (fabio.sobreira@ufpe.br) on 2017-05-16T13:12:17Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação - Tiago Lopes de Araújo - VERSÃO FINAL.pdf: 5049016 bytes, checksum: 19afff51e97123d7092ffd5fd7abcdca (MD5) / Made available in DSpace on 2017-05-16T13:12:17Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação - Tiago Lopes de Araújo - VERSÃO FINAL.pdf: 5049016 bytes, checksum: 19afff51e97123d7092ffd5fd7abcdca (MD5) Previous issue date: 2016-02-29 / CNPQ / O poli(cloreto de vinila) (PVC) é empregado na fabricação de embalagens para alimentos e alguns produtos para saúde. Em geral, esses produtos precisam ser esterilizados antes de serem consumidos. Um dos métodos utilizados para esse fim é a irradiação gama. Todavia, esse tipo de radiação ionizante promove alterações na estrutura das cadeias poliméricas, afetando as propriedades do PVC em maior ou menor grau. Dessa forma, é necessário adicionar determinadas substâncias à resina para estabilizar o material contra a irradiação. O objetivo deste trabalho foi investigar o efeito da radiação gama em filmes de PVC e filmes de PVC contendo 1, 3 e 5 % (m/m) de pentóxido de nióbio (Nb2O5), que é um composto inerte, atóxico e biocompatível. Os filmes foram preparados pela técnica de solution casting, utilizando tetraidrofurano como solvente, e os corpos de prova foram irradiados nas doses de 25 e 50 kGy em temperatura ambiente. Foram utilizadas uma resina de PVC comercial obtida pelo processo de polimerização em suspensão, com massa molar média viscosimétrica igual a 201 kg/mol, e uma amostra de Nb2O5 cujas partículas apresentavam formato irregular, diâmetro volumétrico médio igual a 77 µm e estrutura cristalina monoclínica. Os efeitos da radiação gama e/ou do óxido na matriz polimérica foram avaliados através de viscosimetria de soluções diluídas, colorimetria, ensaio mecânico de tração, análise termogravimétrica (TGA) e espectroscopia no infravermelho médio por transformada de Fourier (FT-MIR). Os resultados da viscosimetria de soluções diluídas mostraram que o percentual de 5 % (m/m) de Nb2O5 conferiu proteção radiolítica ao polímero, diminuindo os eventos de cisão das cadeias principais em relação à matriz de PVC. De acordo com os ensaios colorimétricos, os filmes se tornaram mais escuros e mais amarelados, tanto em função do aumento do percentual de óxido quanto do aumento da dose de radiação. Para o mesmo material, a exposição à radiação gama não causou mudanças significativas nas propriedades mecânicas avaliadas pelo ensaio mecânico de tração (tensão na força máxima, módulo de Young e alongamento percentual na força máxima). Por outro lado, a presença do Nb2O5 nos sistemas contribuiu para diminuir o valor dessas propriedades. Os resultados da TGA mostraram que a radiação gama reduziu a estabilidade térmica dos materiais preparados, enquanto que o óxido não a alterou significativamente. A exposição dos filmes à radiação gama contribuiu para reduzir a energia de ativação do processo de desidrocloração e aumentar a energia de ativação do processo de quebra das sequências de polienos, embora o óxido não tenha catalisado nenhum dos dois processos. Algumas modificações químicas provocadas pela irradiação dos filmes foram detectadas pela espectroscopia FT-MIR, empregando a reflectância total atenuada para a aquisição dos espectros. Também foi constatado que o Nb2O5 não apresentou atividade antibacteriana frente à Escherichia coli, avaliada pelo ensaio de macrodiluição em caldo com agitação. / Poly(vinyl chloride) (PVC) is used in the manufacture of food packaging and some health products. In general, these products need to be sterilized before being consumed. One method for this purpose is gamma irradiation. However, this type of ionizing radiation promotes changes in the structure of polymeric chains affecting PVC properties a greater or lesser extent. Thus, it is necessary to add certain substances to the resin to stabilize the material against the irradiation. The objective of this study was to investigate the effect of gamma radiation on PVC films and PVC films containing 1, 3 and 5 wt% of niobium pentoxide (Nb2O5), which is an inert, non-toxic and biocompatible compound. The films were prepared by solution casting technique using tetrahydrofuran as a solvent and the proof bodies was irradiated at doses of 25 and 50 kGy at room temperature. A commercial PVC resin obtained by suspension polymerization process with viscosimetric average molar mass equal to 201 kg/mol and a Nb2O5 sample whose particles had irregular shape, volume mean diameter of 77 μm and a monoclinic crystalline structure have been used. The effects of gamma radiation and/or oxide in polymer matrix were evaluated using dilute solution viscometry, colorimetry, mechanical tensile test, thermogravimetric analysis (TGA) and Fourier transform middle infrared (FT-MIR) spectroscopy. The results of dilute solution viscometry showed that the percentage of 5 wt% of Nb2O5 conferred radiolytic protection to the polymer, reducing main chain scission events in relation to PVC matrix. According to colorimetric test, the films became darker and yellowish, both due to the increase in oxide percentage as the increase of radiation dose. For the same material, exposure to gamma radiation did not cause significant changes in the mechanical properties evaluated by the mechanical tensile test (tensile strength, Young's modulus and percent elongation). Moreover, the presence of Nb2O5 in systems contributed to reduce the value of these properties. The results of TGA showed that gamma radiation reduced the thermal stability of prepared materials, while the oxide did not change it significantly. Exposure of the films to gamma radiation contributed to reduce the activation energy for the dehydrochlorination process and increase the activation energy for the breakdown process of polyenes sequences, although the oxide has not catalyzed neither processes. Some chemical changes caused by irradiation of the films were not detected by FT-MIR spectroscopy, using attenuated total reflectance to the spectra acquisition. It was also found that Nb2O5 did not presented antibacterial activity against Escherichia coli, evaluated by broth macrodilution test with agitation.

Um estudo refinado dos filmes derivados do gel de pentóxido de vanádio foi realizado por meio de técnicas espectroscópicas e microscópicas visando compreender melhor as características deste material na escala microscópica. Foi demonstrado que o gel de pentóxido de vanádio é uma suspensão de nanopartículas anisotrópicas que se mantêm estáveis mesmo em altas concentrações. As propriedades estruturais e espectroscópicas destas nanopartículas foram revistas e discutidas no estado da arte. Em paralelo foi possível investigar fenômenos como a transição de fase induzida por laser e desenvolver aplicações tecnológicas em áreas como litografia e sensoriamento de gases. Ficou destacada nesta tese o grande potencial de investigação da microscopia Raman confocal na área de nanomateriais. / A refined study of films derived from vanadium pentoxide gel was carried out based on spectroscopic and microscopic techniques, aiming a better understanding of this material on a microscopic scale. It was demonstrated that the vanadium pentoxide gel consists of a suspension of anisotropic nanoparticles which remains stable even at high concentrations. The structural and spectroscopic properties of such nanoparticles were reviewed and discussed, providing new insights at the state of the art. It was also investigated the occurrence of some relevant phenomena, such as the laser induced phase transition, and to develop new technological applications in areas such as gas sensing and lithography. The collection of results described in thesis highlighted a great research potential of confocal Raman microscopy, in the field of nanomaterials.

A chemical ionisation mass spectrometer (CIMS) was developed and utilised for measurements onboard the Facility for Atmospheric Airborne Measurements (FAAM) BAe-146 aircraft. The I- ionisation scheme was implemented to detect nitric acid (HNO3), formic acid (HC(O)OH), hydrogen cyanide (HCN) and dinitrogen pentoxide (N2O5) simultaneously at a sampling frequency of 1 Hz. Sensitivities ranged from 35±6 ion counts pptv-1 s-1 for HC(O)OH to 4±0.9 ion counts pptv-1 s-1 for HCN and limits of detection from 37 ppt for HNO3 and 5 ppt for HCN. Trace gas concentrations of species such as HC(O)OH are currently under predicted in global models. In order to understand their role in controlling air quality, it is crucial that their production pathways and abundance are accurately measured and constrained. To date, airborne measurements of these trace gases have been difficult as a result of instrumental limitations on an aircraft such as limit of detection and sampling frequency. The first UK airborne measurements of HC(O)OH and HNO3 confirmed that HC(O)OH is under predicted by up to a factor of 2 in a trajectory model that implements the full Master Chemical Mechanism (MCM) and Common Representative Intermediate Scheme (CRI). The inclusion of a primary vehicle source enabled the model to reproduce the concentrations observed; verifying that direct sources are under represented. Secondary formation of HC(O)OH was observed through its correlation with HNO3 and ozone (O3), indicating a strong photochemical production source. Hydroxyl (OH) concentrations were estimated for the first time in a flight around the UK using the HC(O)OH and HNO3 measurements. A biomass burning (BB) plume identification technique is applied to data obtained from Canadian biomass fires using HCN as a marker. A 6 sigma above background approach to defining a plume resulted in a higher R2 correlating value for the normalised excess mixing ratio (NEMR) to carbon monoxide (CO) when compared to current methods in the literature. The NEMR obtained from this work; 3.76±0.02 pptv ppbv-1, lies within the range found in the literature. This NEMR is then used to calculate a global emission total for HCN of 0.92 Tg (N) yr-1 when incorporated into the global tropospheric model STOCHEM CRI. The first direct N2O5 airborne measurements on an aircraft at night are compared to indirect measurements taken by a broadband cavity enhancement absorption spectrometer. An average R2 correlation coefficient of 0.87 observed over 8 flights for 1 Hz measurements indicates the selectiveness of the I- ionisation scheme to detect N2O5 directly, without nitrate (NO3) interference.

[pt] A ustulação cloretante é um processo amplamente utilizado no âmbito da metalurgia extrativa, principalmente no que se diz respeito à obtenção de metais. Estudos demonstram que a partir de um agente cloretante gasoso e a incorporação no sistema de um agente redutor, tanto a cinética quanto a termodinâmica das reações são estimuladas. Neste contexto, compostos organoclorados, como CCl4 e C2Cl4, despontam como candidatos promissores à substituição do Cl2. O presente estudo realiza uma avaliação termodinâmica dos processos a partir de diagramas de especiação para o equilíbrio, assim como a modelagem de dados cinéticos associados à cloração do óxido de cobre (CuO - 923 K a 1173 K) e do pentóxido de tântalo (Ta2O5 - 1073 K a 1223 K), em atmosfera de C2Cl4 diluído em N2, mediante o emprego de equações já consolidadas no âmbito da modelagem de reações gás-sólido (núcleo não reagido, auto-catalítico e Avrami). Os modelos do núcleo não reagido com controle difusional pela camada de cinzas e controle químico, foram os dois que apresentaram ajustes de melhor qualidade. O modelo difusional apresentou energia de ativação global para o CuO de 71,5592 mais ou menos 10 kJ.mol(-1) e de 62,2606 mais ou menos 10 kJ.mol (-1) para o Ta2O5, enquanto que com controle químico, para o CuO, obteve-se o valor de 118,0049 mais ou menos 10 kJ.mol(-1) e para o Ta2O5 um valor de 119,131 mais ou menos 10 kJ.mol(-1). Valores consistentes com o que é apresentado na literatura, sendo superiores em modelos com premissa química do que em modelos difusionais. Aspectos físicos também foram considerados e mediante ao número de Reynolds encontrado (Re=0,26 – escoamento laminar), reforçou-se um controle de natureza mista possível para ambos os óxidos. / [en] Chloride roasting is a process widely used in the field of extractive metallurgy, especially with regard to obtaining metals. Studies show that from a gaseous chlorinating agent and the incorporation of a reducing agent in the system, both the kinetics and the thermodynamics of the reactions are stimulated. In this context, organochlorine compounds, such as CCl4 and C2Cl4, stand out as promising candidates for the replacement of Cl2. The present study performs a thermodynamic evaluation of the processes from speciation diagrams for equilibrium, as well as the modeling of kinetic data associated with the chlorination of copper oxide (CuO - 923 K to 1173 K) and tantalum pentoxide (Ta2O5 - 1073 K to 1223 K), in an atmosphere of C2Cl4 diluted in N2, using equations already consolidated in the context of gas-solid reaction modeling (shrinking core, auto-catalytic and Avrami). The models of the shrinking core with diffusional control by the ash layer and chemical control, were the two that presented better quality adjustments. The diffusional model showed global activation energy for the CuO of 71.5592 plus-minus 10 kJ.mol (-1) and 62.2606 plus-minus 10 kJ.mol (-1) for Ta2O5, while with chemical control, for CuO, 118.0049 plus-minus 10 kJ.mol (-1) was obtained and for Ta2O5 a value of 119,131 plus-minus 10 kJ.mol (-1). Values consistent with what is presented in the literature, being higher in models with chemical premise than in diffusion models. Physical aspects were also considered and, based on the Reynolds number found (Re = 0,26 - laminar flow), a control of mixed nature possible for both oxides was reinforced.

<p>Electrospinning has gained immense interests in recent years due to its potential application in various fields, including energy storage application. The V₂O₅/GO as a layered crystal structure has been demonstrated to fabricate nanofibers with diameters within a range of ~300nm through electrospinning technique. The porous, hollow, and interconnected nanostructures were produced by electrospinning formed by polymers such as Polyvinylpyrrolidone (PVP) and Polyvinyl alcohol (PVA), separately, as solvent polymers with electrospinning technique. </p> <p> </p> <p>In this study, we investigated the synthesis of a graphene-modified nanostructured V₂O₅ through modified sol-gel method and electrospinning of V₂O₅/GO hybrid. Electrochemical characterization was performed by utilizing Arbin Battery cycler, Field Emission Scanning Electron Microscopy (FESEM), X-ray powder diffraction (XRD), Thermogravimetric analysis (TGA), Mercury Porosimetery, and BET surface area measurement. </p> <p> </p> <p>As compared to the other conventional fabrication methods, our optimized sol-gel method, followed by the electrospinning of the cathode material achieved a high initial capacity of <b>342 mAh/g</b> at a high current density of 0.5C (171 mA/g) and the capacity retention of ~80% after 20 cycles. Also, the prepared sol-gel method outperforms the pure V₂O₅cathode material, by obtaining the capacity almost two times higher.</p> <p>The results of this study showed that post-synthesis treatment of cathode material plays a prominent role in electrochemical performance of the nanostructured vanadium oxides. By controlling the annealing and drying steps, and time, a small amount of pyrolysis carbon can be retained, which improves the conductivity of the V₂O₅ nanorods. Also, controlled post-synthesis helped us to prevent aggregation of electro-spun twisted nanostructured fibers which deteriorates the lithium diffusion process during charge/discharge of batteries.</p>

Made available in DSpace on 2016-08-31T13:33:45Z (GMT). No. of bitstreams: 1 DaniloS_Dissert.pdf: 5168115 bytes, checksum: 4eef89b1faaafc0dc7f33e05bfdaa190 (MD5) Previous issue date: 2015-08-28 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work studied the application of niobium pentoxide (Nb2O5) individually as substrate of microstrip antennas, when processed by powder technology. Powder with a particle size D50 of 40 &#120583;m Nb2O5 was compressed in the pressure of 55 MPa, 111 MPa and 166 MPa and was sintered at temperatures of 800 ° C, 900 ° C, 1000 ° C and 1100 ° C for 4 h. Subsequently, the processed samples were characterized electricaly, physicaly and mechanicaly. In electrical characterization were obtained they loss tangent values and permittivity in two frequency bands (0,2 GHz to 4,0 GHz and 8,2 GHz to 12,4 GHz). In mechanical characterization, the tensile strength limit was calculated indirectly by diametrical compression test. In the physical characterization, their porosity, mass percentage variations and dimensional variations values were calculated. In addition, samples were characterized by the methods of X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. Devices were also made with the produced substrates. These were characterized in the frequency range of 2,0 GHz to 14,0 GHz. Subsequently, several observations and conclusions were made. Among the main ones are: all made devices functioned as an antenna; the variation of the parameters of the manufacturing process resulted in changes in the electrical properties of the substrates, and consequently made the operating parameters antennas; all of the substrates produced seemed slightly weak and little mechanically resistant; the values of permittivity and loss tangent were according with the indications of the bibliography / O presente trabalho estudou a aplicação do pentóxido de nióbio (Nb2O5) individualmente como substrato de antenas de microfita, quando processado pela tecnologia do pó. O Pó com granulometria D50 40 &#120583;m do Nb2O5 foi compactado nas pressões de 55 MPa, 111 MPa e 166 MPa e foi sinterizado nas temperaturas de 800 °C, 900 °C, 1000 °C e 1100 °C, durante 4 h. Subsequentemente, as amostras processadas foram caracterizadas elétrica, estrutural e mecanicamente. Na caracterização elétrica, foram obtidos valores da tangente de perdas e da permissividade elétrica em duas faixas de frequência (de 0,2 GHz a 4,0 GHz e de 8,2 GHz 12,4 GHz). Na caracterização mecânica, o limite de resistência à tração foi calculado indiretamente pelo ensaio de compressão diametral. Na caracterização estrutural, foram calculados valores de porosidade e de variações percentuais mássicas e dimensionais. Além disso, as amostras foram caracterizadas pelos métodos de difração de raios-X, de microscopia eletrônica de varredura e de espectroscopia de energia dispersiva. Também foram confeccionados dispositivos com os substratos produzidos. Esses foram caracterizados na faixa de frequência de 2,0 GHz a 14,0 GHz. Dentre as conclusões obtidas, pode-se destacar que todos os dispositivos confeccionados funcionaram como antena; a variação dos parâmetros do processo de fabricação acarretou na variação das propriedades elétricas dos substratos e, consequentemente, nos parâmetros de funcionamento das antenas confeccionadas; os substratos produzidos se mostraram todos frágeis e pouco resistentes mecanicamente; os valores da permissividade elétrica e da tangente de perdas que foram obtidos condisseram com as indicações da bibliografia consultada

Studium transportu náboje v Ta2O5 oxidových nanovrstvách se zaměřuje především na objasnění vlivu defektů na vodivost těchto vrstev. Soustředíme se na studium oxidových nanovrstev Ta2O5 vytvořených pomocí anodické oxidace. Proces výroby Ta2O5 zahrnuje řadu parametrů, jež ovlivňují koncentraci defektů (oxidových vakancí) v této struktuře. Vrstva oxidu Ta2O5 o tloušťce 20 až 200 nm se často používá jako dielektrikum pro tantalové kondenzátory, které se staly nedílnou součástí elektrotechnického průmyslu. Kondenzátory s Ta2O5 dielektrickou vrstvou lze modelovat jako strukturu MIS (kov – izolant – polovodič). Anodu tvoří tantal s kovovou vodivostí, katodu potom MnO2 či vodivý polymer (CP), které jsou polovodiče. Hodnoty elektronových afinit, respektive výstupních prací, jednotlivých materiálů potom určují výšku potenciálových bariér vytvořených na rozhraních kov-izolant (M – I) a izolant-polovodič (I – S). Dominantní mechanizmy transportu náboje lze určit analýzou I-V charakteristiky zbytkového proudu. Dominantní mechanizmy transportu náboje izolační vrstvou jsou ohmický, Poole-Frenkelův, Shottkyho a tunelování. Uplatnění jednotlivých vodivostních mechanismů je závislé na teplotě a intenzitě elektrického pole v izolantu. Hodnota zbytkového proud je významným indikátorem kvality daného izolantu. Ten závisí na technologii výroby kondenzátoru, významně především na parametrech anodické oxidace a na materiálu katody. I-V charakteristiky zbytkového proudu se měří v normálním a reversním módu, tj. normální mód značí kladné napětí na anodě a reversní mód záporné napětí na anodě. I-V charakteristika je výrazně nesymetrická, a proto tyto kondenzátory musí být vhodně polarizovány. Nesymetrie I-V charakteristiky se snižuje s klesající teplotou, při teplotě pod 50 K a je možno některé kondenzátory používat jako bipolární součástky. Z analýzy I-V charakteristiky lze určit řadu parametrů, jako tloušťku izolační vrstvy a koncentraci defektů v izolační Ta2O5 vrstvě a dále lze odhadnout parametry MIS modelu kondenzátoru - stanovit hodnotu potenciálových bariér na rozhraních M – I a I – S. Měření C-V charakteristik při různých teplotách v rozsahu 10 až 300 K je využíto pro určení výšky potenciálové bariéry na rozhraní I – S, závislosti kapacity na teplotě a dále pro výpočet efektivní plochy elektrod. Z výbrusu vzorků na skenovacím elektronovém mikroskopu byly určeny tloušťky dielektrika Ta2O5 pro jednotlivé vyhodnocované řady kondenzátorů.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Since 1990s, rechargeable Li-ion batteries have been widely used in consumer electronics such as cell phones, global positioning systems (GPS), personnel digital assistants (PDA), digital cameras, and laptop computers. Recently Li-ion batteries received considerable attention as a major power source for electric vehicles. However, significant technical challenges still exist for widely deploying Li-ion batteries in electric vehicles. For instance, the energy density of Li-ion batteries is not high enough to support a long-distance commute. The Li-ion batteries used for the Nissan Leaf and Chevy Volt only can support 50 – 100 miles per charge. The cost of Li-ion battery packs in electric vehicles is still high. The battery pack for the Chevy Volt costs about $8,000, and the larger one in the Nissan Leaf costs about $12,000. To address these problems, new Li-ion battery electrode materials with high energy density and low cost should be developed. Among Li-ion battery cathode materials, vanadium pentoxide, V2O5, is one of the earliest oxides studied as a cathode for Li-ion batteries because of its low cost, abundance, easy synthesis, and high energy density. However, its practical reversible capacity has been limited due to its irreversible structural change when Li insertion is more than x = 1. Tremendous efforts have been made over the last twenty years to improve the phase reversibility of LixV2O5 (e.g., 0 ≤ x ≤ 2) because of vanadium pentoxides’ potential use as high capacity cathodes in Li-ion batteries. In this thesis, a new strategy was studied to develop vanadium pentoxide cathode materials with improved phase reversibility. The first study is to synthesize vanadium oxide cathodes via a new chemical route – creating a phase transformation from the vanadium sulfide to oxide. The β-Na0.33V2O5 was prepared via a new method of chemical synthesis, involving the chemical transformation of NaVS2 via heat-treatment at 600 °C in atmospheric air. The β-Na0.33V2O5 particles were well crystalized and rod-shaped, measuring 7–15 μm long and 1–3 μm wide with the formation of the crystal defects on the surface of the particles. In contrast to previous reports contained in the literature, Na ions were extracted, without any structural collapse, from the β -Na0.33V2O5 structure and replaced with Li ions during cycling of the cell in the voltage range, 1.5 V to 4.5 V. This eventually resulted in a fully reversible Li intercalation into the LixV2O5 structure when 0.0 ≤ x ≤ 2.0. The second study is to apply the synthesis method to LiVS2 for the synthesis of β׳-LixV2O5 for use as a high performance cathode. The synthesis method is based on the heat treatment of the pure LiVS2 in atmospheric air. By employing this method of synthesis, well-crystalized, rod-shaped β׳-LixV2O5 particles 20 – 30 μm in length and 3 – 6 μm in width were obtained. Moreover, the surface of β׳-LixV2O5 particles was found to be coated by an amorphous vanadium oxysulfide film (~20 nm in thickness). In contrast to a low temperature vanadium pentoxide phase (LixV2O5), the electrochemical intercalation of lithium into the β׳-LixV2O5 was fully reversible where 0.0 < x < 2.0, and it delivered a capacity of 310 mAh/g at a current rate of 0.07 C between 1.5 V and 4 V. Good capacity retention of more than 88% was also observed after 50 cycles even at a higher current rate of 2 C. The third study is the investigation of NaVS2 as a cathode intercalation material for sodium ion batteries. We have shown that reversible electrochemical deintercalation of x ~ 1.0 Na per formula unit of NaxVS2, corresponding to a capacity of ~200 mAh/g, is possible. And a stable capacity of ~120 mAh/g after 30 cycles was observed. These studies show that the new chemical synthesis route for creating a phase transformation from the vanadium sulfide to oxide by heat treatment in air is a promising method for preparing vanadium oxide cathode material with high reversibility. Although this sample shows a relatively low voltage range compared with other cathodes such as LiCoO2 (3.8 V) and LiFePO4 (3.4 V), the large capacity of this sample is quite attractive in terms of increasing energy density in Li-ion batteries. Also, NaVS2 could be a promising cathode material for sodium ion batteries.