Pyrochlore microdomain formation in fluorite oxides

The pyrochlore microdomain formation in the fluorite lattice was investigated by means of electron microscope techniques, especially for the system (TbxGd1−x)2 Zr2O7+y (0 x 1; 0 y < 0.25). Specimens with x> 0.2 or specimens with x 0.2 which were quenched from temperatures above the order-disorder transition temperature show diffuse scattering in the electron diffraction images, remarkably similar to diffuse scattering observed for other defect fluorite oxides. The diffuse scattering is discussed in terms of the formation of a small basic cluster in the fluorite lattice. Annealed specimens with x 0.2 show pyrochlore diffraction spots and microdomain formation. The domains have an average diameter ranging from a value smaller than 10 nm for x = 0.2 up to 100 nm for Gd2Zr2O7. The domains grow in a disordered (fluorite) matrix and finally form antiphase boundaries. The transition from the basic cluster to a well-developed microdomain is not yet clear. The observed microdomain structure is used to explain the results of oxygen ion conductivity experiments

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part I: Experimental methods and current-overvoltage experiments

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd2Zr2O7 (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m2). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process

Study of the oxygen electrode reaction using mixed conducting oxide surface layers. Part II: Small signal analysis

The oxygen gas electrode has been studied for a number of mixed conducting oxide surface layers on top of Gd2Zr2O7 (TGZO) solid electrolytes. In part II of this paper we present the results of frequency dispersion measurements for the electrode reaction, supplying additional information to the results of current-overvoltage experiments presented in part I. For both kinds of experiments the same trends were observed for the electrode polarization. Best results are obtained for a surface layer of TGZO, while p-type mixed conducting oxides give less decreased values of the electrode polarization. High electrode capacitances were found in the case of mixed conducting surface layers (about 700 F/m2). The electrode reactions follow a Butler-Volmer type of equation. Most probably a diffusion process is rate controlling the overall charge transfer process

Oxygen ion and mixed conductivity in compounds with the fluorite and pyrochlore structure

The effect of pyrochlore order in solid solutions with the defect fluorite structure was studied. The amount of order was changed by various heat treatments or by varying the cation composition. Examples of short range order and microdomain-formation have been observed in Tb2Zr2O7+x and Gd2Zr2O7. Pyrochlore order results in a decrease of the activation enthalpy and pre-exponential factor for oxygen ion conduction. The results are explained by a model based on the occurrence of a preferential diffusion path with a low strain energy component in ΔH. Optimal conductivity is achieved in materials which are not completely ordered. Mixed conductivity in Ln2Zr2O7 with P structure can be realized by partial replacement of Ln by Tb. This results in good ionic as well as electronic conductivities

Defect structures and migration mechanisms in oxide pyrochlores

Using computer simulation techniques the defect structure and oxygen ion migration mechanism of oxide pyrochlores (eg. Gd2Zr2O7) was investigated in order to explain the decreased activation enthalpy for oxygen ion conductivity as a function of order. Shell model potentials were found to be necessary in order to obtain sufficiently accurate physical properties for the pyrochlore compound. The oxygen Frenkel defect consisting of ‘a split 48f vacancy’ and 8b interstitial appeared to be the most stable instrinsic defect, but vacancies related to extended defect structures may play an important role in the diffusion mechanism too. The migration mechanism of oxygen ions is mainly based on 48f-48f jumps and involve 0.9 eV barrier energy, comparable with the experimental activation enthalpies of 70–85 kJ/mol

Urban management and institutional change: An integrated approach to achieving ecological cities

In this contribution I will deal with the following topics in this order: 1. Urban Management an integrated approach! 2. Reforms to improve the performance of the municipality 3. What is new in Urban Management: the New Public Management 4. Autonomy OK, but what is accountability? 5. What are the issues? Lets analyze it 6. What about the dynamics of cities? 7. How can we finance urban development alternatively? 8. Who is the real urban manager and what are some relevant books on urban management? 9. An illustration: solid waste issues in Africaii 10. How can we achieve ecological cities

Van ontwikkelingshulp naar internationale samenwerking

In 1965 kreeg Nederland de eerste minister voor 'ontwikkelingshulp' (Theo Bot). Dat werden later ministers voor ontwikkelingssamenwerking en nu hebben we een minister voor Buitenlandse Handel, ontwikkelingssamenwerking. Dat is de koopman en de dominee in één werd er al gespot. Hier ligt een ontwikkeling in ons denken over armoede en ontwikkelingslanden aan ten grondslag die besproken zal worden. Dat denken is sterk beïnvloed door de snelle ontwikkeling in Azië, de belangrijke rol van de particuliere sector daarin (commercieel en niet-gouvernementeel), kritiek op de traditionele ontwikkelingssamenwerking en recentelijk door de rol van China en India als donoren in het tegenwoordig ook snel groeiende Afrika. Die nieuwe minister van NGO en PVDA huize (mevr. Ploumen) kreeg gelijk ruzie met de minister van economische zaken (Kamp) over de besteding van die één miljard 'bezuinigingen', in een zaak die heel duidelijk het verschil in achtergrond van beide politici verraadt (Financieel Dagblad 6-11-12). De overgang naar internationale samenwerking heeft nogal wat implicatie

Public–private partnerships in basic service delivery: impact on the poor, examples from the water sector in India

What is the theory behind Public–Private Partnerships (PPPs)? In this contribution PPPs are defined as private sector involvement, where a public and a private partner share the risks related to the necessary investments. Besides complementarity, the other factors contributing to the success of PPPs will be analysed. Evidence concerning India will be used to assess which factors played a role and to suggest a PPP dialogue in India, which would involve all stakeholders before actually embarking on PPPs for urban infrastructure projects such as drinking water and sanitation. It would help to do projects in such a way that they would also benefit the urban poor

Decentralization and basic services provision: water and sanitation in Ghana

How does decentralization reform affect the provision of basic services, particularly water and sanitation in Ghana? We deal in particular the delivery of water and sanitation, given the importance of water and sanitation. Conclusions are drawn concerning the policy implications for the design and implementation of decentralization reform. The first is the need to ensure that laws establishing service delivery agencies and possible partnership arrangements are consistent with the specific laws that set out the nature decentralization reform. The second policy implication of our study is the need for a conscious implementation plan in support of decentralization laws and policies. The policy implication regards the question of appropriate roles by local government. We have observed that pluralism performs better that distributed monopoly by public utilities. Decentralization reforms should deepen local accountability in the provision of basic services. Finally, assigning leadership, brokerage and oversight roles to local government in the design of decentralization reforms is critical for expanding basic services

Role of small-scale independent providers in water and sanitation

Small-scale independent providers (SSIPs) and households are good for 10–69% of the household water supply and sometimes up to 95% of the sanitation solutions in cities in developing countries. Different types of SSIP can be distinguished. They could be allowed to make a more important contribution to drinking water and sanitation in a situation where many governments cannot be the only one to supply drinking water and sanitary services. Theoretical and practical arguments are used to explain why private sector involvement is even more frequent in sanitation than in drinking water. The issue of how to improve the efficiency in the water and sanitation sector will be raised by looking at ways to unbundle sanitation, to use technological innovations and to bring in more competition. The need for alternative technologies is stressed, since a fully fledged sewerage system in every Third World city would contribute to increased foreign debt in many countries, given that the steel and cement often need to be imported