Dopant additive

Fig. 4. Effect of dopant additions on the resistivity versus temperature behavior of BaTiO PTCR ceramics. A, undoped B, doped with 0.134 mol % Cr ...

In general, dopant additions decrease the grain boundary mobility. Horn and Messing reported small increases in Mg as a result of Ti doping. The pronounced effect of adding Ti + observed in the present case is clearly unexpected, since it suggests that doping leads to an increase... 

Catalytic rans carried out changing the temperature showed, for all the catalysts, that while conversion increases with the increasing temperature, selectivities do not depend on it. The temperature at which a 50% conversion is attained was 543 K for ZrOj Upon dopant addition a decrease in conversion was observed for all the catalysts, the temperature for 50% conversion being in the range 593-673 K. 

Up to now there has been no general theory for the description and prediction of heterogeneous catalytic processes. The reason is the complexities of real systems, which consist of numerous components, including structure and dispersion stabilizers, dopants, additives for increased selectivity, and many others. Therefore, there is great need for research on the behavior of catalyst surfaces that consist of several components [4]. The fundamental knowledge required, for example, to improve the selectivity of catalysts is also lacking. 

In diffusion-controlled sintering, since atom diffusivity and, thus, atom mobility increases with an increased vacancy concentration, we can enhance sintering kinetics by increasing the vacancy concentration. For ionic compounds, vacancy concentration varies considerably with dopant addition. (See Section 13.1.)... 

In the case of lattice diffusion, the effective diffusion coefficient can vary considerably with the addition of a dopant because the dopant addition can drastically change the concentration of defects, as explained in Chapter 12. Consider, as an example, an MO oxide with vacancies as major defects. If the activation energy of cation vacancy diffusion, lower than that of anion... 

Su X-T, Yan Q-Z, Ma Y-H, Zhang W-F and Ge C-C (2006), Effect of co-dopant addition on the properties of yttrium and neodymium doped barium cerate electrolyte . Solid State Ionics, 177,1041-1045. 

The addition of foreign metal oxides beyond their solubility limits may hinder the Sn02 grain growth and then contribute to enhance the gas response also by the grain size effect. To make clear the role of dopants (additives), detailed investigation is, of course, indisjrensable. 

Not only pure Ti02 but also composite photocatalysts have been widely investigated. A mixture of Ti02 precursors (or sol) and other metal oxide precursors (or sol) gives an inorganic composite film. As mentioned below (additionally, Section Composites and dopant additions ), various compositions as a powder or a film have been prepared in order to improve photocatalytic activities and/or photoinduced superhydrophilic properties. 

All the samples, regardless of sintering conditions and dopant addition have not shown any cracking or distortion after sintering. XRD phase analysis showed that through the sintering of MgO-doped and undoped HA samples, no secondary phases such as TCP, CaO and calcium hydroxide were verified as shown in Figure 1. 

Continuing interest is apparent also in other dopants, additional to Zn , for catalytic fluorination of CCl2=CCl2 leading to CHF2CF3 and its relatives, La being the most active... 

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