En la presente memoria se describe el método para la medida de la variación térmica de la resistividad entre 10 y 300 K que hemos puesto a punto en nuestros laboratorios de la Universidad de Cantabria. Dicho método es el de cuatro puntas con corriente alterna y detección síncrona. También se analizan, mediante el método de los elementos finitos, los efectos de la geometría de la muestra y posición de los contactos en la relación entre la resistividad observada experimentalmente y la resistividad real, haciendo hincapié en el caso de muestras anisótropas. Posteriormente aplicamos esta técnica al estudio de diversas series de materiales: 1) Los compuestos RPt que cumplen la Ley de De Gennes y en los que hemos podido determinar los valores de la masa efectiva m* y de la constante de canje. 2) Los compuestos RNi2Si2 en las que se puede observar una relación entre la resistividad magnética y las estructuras magnéticas. 3) Los compuestos CeyLa1-yNixPt1-x, en las que se estudia el efecto Kondo 4) Los amorfos metálicos (Co1-x(Fe5Ni5)x)75Si15B10 en los que se observa un mínimo en la resistividad a bajas temperaturas así como variaciones en lnT, T2 y T a temperaturas bajas, intermedias y altas respectivamente / The present report describes the method for measuring the temperature dependence of the resistivity between 10 and 300 K that we have developed in our laboratories at the University of Cantabria. This is a four-probe method using ac current and synchronous detection. Also it is analyzed, using the finite element method, the effects of the sample geometry and contacts position in the relationship between the real resistivity and resistivity observed experimentally, even in the case of anisotropic samples. Subsequently we apply this technique to the study of different family of materials: 1) RPt compounds which follow the De Gennes Law, allowing us to determine the values of the effective mass m * and exchange constant. 2) The compounds RNi2Si2 in which it is possible to establish a relationship between the magnetic resistivity and the magnetic structures. 3) The compounds CeyLa1-yNixPt1-x, in which we study the Kondo effects. 4) The amorphous Co1-x(Fe5Ni5)x)75Si15B10 metals, in which there is a minimum in the resistivity at low temperatures as well as variations in LnT, T2 and T at low, intermediate and high temperatures respectively.

The ability to tune the properties over a wide range of values by changing the additives, composition, etc., has made chalcogenide glassy semiconductors, most interesting from both fundamental physics as well as technology point of view. In particular, the occurrence of the two network topological thresholds namely the Rigidity Percolation Threshold (RPT) and the Chemical Threshold (CT) and their influence on various properties of chalcogenide glasses have been of immense interest during the last three decades. The Rigidity Percolation Threshold (also known as the Stiffness Threshold or Mechanical Threshold) corresponds to the composition at which the material transforms from a floppy polymeric glass to a rigid amorphous solid, whereas at Chemical Threshold the sample tends towards an ordered state. Though the rigidity percolation has been considered for long to occur at a critical threshold defined by the constraint’s theory, the recent theoretical and experimental investigations have found the RPT to occur over a range of compositions. In systems exhibiting an extended rigidity percolation, two distinct transitions namely from a floppy to an isostatically rigid phase and from an isostatically rigid to a stressed rigid phase are seen. In the category of chalcogenide glasses, tellurides have been found to exhibit interesting properties including the phenomenon of electrical switching which finds applications in Phase Change Memories (PCM). Studies on various thermal, electrical and photoelectrical properties of glassy tellurides help us in identifying suitable materials for different technological applications. This thesis deals with Differential Scanning Calorimetric (DSC) & Temperature Modulated Alternating Differential Scanning Calorimetric (ADSC) studies, electrical switching investigations, photoconductivity & photothermal measurements on certain metal doped telluride glasses. The composition dependence of properties such as glass transition & crystallization temperatures, switching voltage, thermal diffusivity, photosensitivity, etc., have been analyzed to obtain information about topological thresholds, thermally reversing window, etc. The first chapter of thesis provides an overview of properties of amorphous semiconductors, in particular chalcogenide glasses. The local & defect structure, the electronic band structure & electrical properties, electrical switching behavior, etc., are discussed in detail. The theoretical aspects related to the experiments undertaken in this thesis work have also been described. The instrumentation used for various experiments conducted to measure thermal, electrical, photoelectrical and photothermal properties have been discussed in chapter two. The chapter three deals with the photocurrent measurements on As40Te60-xInx (7.5 ≤ x ≤ 16.5) glasses. In these samples, it has been found that the photocurrent increases with illumination, which is understood on the basis of the large dielectric constant and also due to the presence of a large number of positively charged defect states. Further, the composition dependence of the conductivity activation energy and the photosensitivity exhibit a maximum at x = 12.5 (<r> = 2.65) and a minimum at x = 15.0 (<r> = 2.70) which has been identified to be the Rigidity Percolation Threshold (RPT) and the Chemical Threshold (CT) respectively. The results of electrical switching, DSC and Photothermal Deflection (PTD) studies on As20Te80-xGax (7.5 ≤ x ≤ 18.5) glasses, undertaken to elucidate the network topological thresholds, are described in chapter four. It has been found that all the As20Te80-xGax glasses studied exhibit memory type electrical switching. The switching voltage (VT) of these glasses increases monotonically with x, in the composition range 7.5 ≤ x ≤ 15.0. The increase in VT with gallium addition leads to a local maximum at x = 15.0 and VT decreases with x thereafter, reaching a distinct minimum at x = 17.5. Based on the variation with composition of the electrical switching voltages, the composition x = 15.0 and x = 17.5 have been identified to be the rigidity percolation and chemical thresholds of the As20Te80-xGax glassy system respectively. Further, the DSC studies indicate that As20Te80-xGax glasses exhibit a single glass transition (Tg) and two crystallization reactions (Tc1 & Tc2) upon heating. There is no appreciable change in Tg of As20Te80-xGax glasses with the addition of upto about10 atom% of Ga, whereas a continuous increase is seen in the crystallization temperature (Tc1). It is interesting to note that both Tg and Tc1 exhibit a maximum at x = 15.0 and a minimum at x = 17.5, the compositions identified to be the RPT and CT respectively by the switching experiments. The composition dependence of thermal diffusivity estimated from the PTD signal, indicate the occurrence of an extended stiffness transition in As20Te80-xGax glasses, with the compositions x = 9.0 and x = 15.0 being the onset and the completion of an extended rigidity percolation. A maximum and a minimum are seen in the thermal diffusivity respectively at these compositions. Further, a second maximum is seen in the thermal diffusivity of As20Te80-xGax glasses, the Chemical Threshold (CT) of the glassy system. The fifth chapter of the thesis describes the ADSC, electrical switching and photocurrent measurements on Ge15Te85-xInx (1 ≤ x ≤ 11) glasses. It is found there is not much change in the Tg of Ge15Te85-xInx glasses in the composition range 1 ≤ x ≤ 3. An increase is seen in Tg beyond x = 3, which continues until x = 11. Further, the composition dependence of non-reversing enthalpy shows the presence of a thermally reversing window in the compositions range x = 3 and x = 7. Electrical switching studies indicate that Ge15Te85-xInx glasses exhibit threshold type of switching at input currents below 2 mA. It is observed that switching voltages decrease initially with indium addition, exhibiting a minimum at x = 3, the onset of the extended rigidity percolation as revealed by ADSC. An increase is seen in VT above x = 3, which proceeds till x = 8, with a change in slope (lower to higher) seen around 7 atom% of indium which corresponds to the completion of the stiffness transition. The reversal in trend exhibited in the variation of VT at x = 8, leads to a well defined minimum around x = 9, the chemical threshold of the Ge15Te85-xInx glassy system. Photocurrent measurements indicate that there is no photodegradation in Ge15Te85-xInx glasses with x < 3, whereas samples with x ≥ 3 show photodegradation behavior. The composition dependent variation in the glass transition temperature has been attributed for this behavior. Further, the composition dependence of photo sensitivity has been found to show the signatures of the extended rigidity percolation and the chemical threshold in Ge15Te85-xInx glasses. The last chapter of thesis (chapter six) summarizes the results obtained and also the scope of future work to be undertaken.

Submitted by Nilo Almeida (naajrj@gmail.com) on 2018-08-15T16:34:00Z No. of bitstreams: 1 The Related Party Transaction in Brazilian Infrastructure PPPs - Final Version.pdf: 1720313 bytes, checksum: 169661514312285f50c2683e8bb457ca (MD5) / Approved for entry into archive by GILSON ROCHA MIRANDA (gilson.miranda@fgv.br) on 2018-08-24T14:47:09Z (GMT) No. of bitstreams: 1 The Related Party Transaction in Brazilian Infrastructure PPPs - Final Version.pdf: 1720313 bytes, checksum: 169661514312285f50c2683e8bb457ca (MD5) / Made available in DSpace on 2018-08-27T14:37:34Z (GMT). No. of bitstreams: 1 The Related Party Transaction in Brazilian Infrastructure PPPs - Final Version.pdf: 1720313 bytes, checksum: 169661514312285f50c2683e8bb457ca (MD5) Previous issue date: 2018-05-11 / Transações com parte relacionadas (RPT) é um problema recorrente na maioria das empresas com propriedade compartilhada porque, ao mesmo tempo que pode trazer uma redução significante dos custos de transação, por outro lado apresenta o risco de ser abusada causando perdas para os acionistas minoritários e credores. A Parceria Público Privada (PPP) de infraestrutura, sendo um empreendimento em sociedade, está sujeito a este dilema e, devido à alavancagem proporcionada pelo Project Finance, há inclusive maiores incentivos ao comportamento oportunista. Um exemplo recente, motivando a discussão, é o case da usina hidroelétrica Santo Antônio, que, com um orçamento inicial de R$ 12 bilhões, acabou custando um total de R$ 20 bilhões. O potencial de retorno imediato por expropriação dos custos majoritários, tipo aquisição e construção para o projeto, na maioria das vezes é extremamente superior à exposição do agente oportunista às perdas durante a futura operação da infraestrutura. Neste trabalho é proposto um modelo microeconômico simples para explorar os incentivos subjacentes nos projetos de PPP com o objetivo de encontrar alternativas para mitigar o desalinhamento de incentivos causados por RPT’s nas PPPs. Finalmente, a literatura pesquisada, em conjunto com o modelo proposto, são usados na comparação com dados empíricos mostrando forte evidência de efeitos negativos das RPTs. Em muitas PPPs no Brasil, a presença de grandes construtoras nas holdings dos seus controladores, aliada à pouca experiência dos agentes governamentais e deficiência de recursos na utilização do modelo PPP, criou um ambiente muito desfavorável ao sucesso desses projetos. / The Related Party Transaction (RPT) is a recurring issue in most shared ownership companies because, at the same time, it has the potential to bring significant reduction of transaction costs, on the other hand, presents many pitfalls of being abused to the loss of the minority shareholders and creditors. The infrastructure Public Private Partnership (PPP), being a shared enterprise, is prone to this dilemma and, because project finance is extremely leveraged, there are even stronger incentives for opportunistic behavior. As a recent example to motivate the discussion there is the case of Santo Antonio hydroelectric power generation facility, which had an initial budget of R$ 12 billion and ended up costing a grand total of R$ 20 billion. The potential immediate returns of expropriation from major expenses, such as acquisition and construction for the project, most of the time, far outweighs the opportunist’s exposure to losses in the future operation of the infrastructure. It is proposed a simple microeconomic model for exploring the underlying incentives of PPP projects to help devise options for mitigating the incentive misalignment of RPTs in PPPs. Finally, the literature and the proposed model findings are used to compare with empirical data which has showed strong evidence of negative RPT effects. In many PPPs in Brazil, the presence of big construction firms in the controlling shareholders’ holdings, coupled with the government’s lack of experience and adequate resources to work with the PPP model, created a difficult environment for the financial success of those projects.