**10. References**


such as high-temperature superconductivity and colossal magnetoresistance observed in these compounds makes them very attractive from both fundamental and applied

There are different methods of synthesis. Among them, one of the most used is that known as ceramic method, although not the most efficient one. The freeze-drying method offers purer materials by reducing the heating time and working at not so high

The general chemical formula for perovskite compounds is *AB*X3, where *A* and *B* are two cations of very different sizes, and X is an anion that bonds to both. The *A* atoms are larger than the *B* atoms. The ideal cubic-symmetry structure has the *B* atoms in 6-fold coordination, surrounded by an octahedron of anions, and the *A* atoms in 12-fold cuboctahedral coordination. The relative ion size requirements for stability of the cubic structure are quite stringent, so slight buckling and distortion can produce several lowersymmetry distorted versions, in which the coordination numbers of *A* cations, *B* cations or both are reduced. The orthorhombic and tetragonal phases are the most common non-cubic

The X-ray diffraction pattern of a pure substance is like a fingerprint of the substance. The powder diffraction method is thus ideally suited for characterization and identification of

The Rietveld method allows us to characterize the polycrystalline materials by a least squares approach to refine a theoretical line profile until it matches the measured profile

It is possible to go further in the study of the structure of the perovskites by means of neutron diffraction, although it is true to say that large facilities are needed to carry out such

The author of this chapter thanks Professors Pedro Núñez and Cristina González-Silgo at Universidad de La Laguna (Spain), and Professor John E. Greedan at McMaster University (Canada) for such important contributions to the field of the perovskites which came strongly in useful for the development of his knowledge of it as well as for having been

Bragg, W.L. (1913). The diffraction of short electromagnetic waves by a crystal, *Proceedings of* 

Coey, J.M.D., Viret, M., von Molnar, S. (1999). Mixed-valence manganites*, Advances in* 

Cullity, B.D. (1977). Elements of X-ray diffraction, Addison-Wesley, 2nd ed., ISBN 0-201-

*the Cambridge Philosophical Society*, Vol.17, pp. 43-57

*Physics*, Vol.48 (2), pp. 167–293. doi:10.1080/000187399243455

polycrystalline phases, and therefore of perovskites.

remarkable mentors during his years of research.

perspectives.

temperatures.

variants.

study.

shown in the pattern.

**9. Acknowledgment** 

**10. References** 

01174-3


**6** 

*China* 

Zhong Xin and Yaoqi Shi

**Controlled Crystallization of Isotactic** 

*State Key laboratory of Chemical Engineering, College of Chemical Engineering, East China University of Science and Technology, Shanghai* 

**Polypropylene Based on α/β Compounded** 

**Nucleating Agents: From Theory to Practice** 

Isotactic polypropylene (iPP) is one of the most important thermoplastic polymers owing to its low manufacturing cost and versatile properties. Moreover, iPP exhibits a very interesting polymorphic behavior (Awaya, 1988; Busse et al., 2000; Lotz et al., 1996; Vagar, 1992). At least five modifications: monoclinic α form, trigonal β form, orthorhombic γ form, δ and smectic phase have been reported. The α form is the best known and most stable in commercial grades of iPP being found in most melt crystallized specimens, especially those being added α Nucleating agents (NA) (Labour et al., 1999; Vagar, 1986). The β form is metastable thermodynamically and is obtained under some special conditions such as a high degree of supercooling, temperature gradient, shear-induced crystallization or addition of βnucleating agents (Fillon et al., 1993; Ismail & Al-Raheil, 1998). The γ form occurs in lowmolecular-weight iPP or under high pressure and the mesomorphic form results from quenching (Meille et al., 1990; Lotz et al., 1986). Different crystalline form of iPP leads

NA as one of the additives presents a role of increasing the nucleation density of polymer greatly and enhancing the nucleation rate dramatically so as to have a great impact on the mechanical properties of polymer (Kristiansen et al., 2003; Romankiewicz et al., 2004; Tenma & Yamaguchi, 2007). So far, two kinds of NAs, α phase and β phase NAs discriminated by the form of iPP they induce have been widely put into use in modifying iPP. The α phase NA can improve the stiffness and optical properties of iPP while decrease its toughness (Gui et al., 2003; Zhang G.P. et al., 2003; Zhang Y.F. & Xin, 2006). The β phase NA will induce βiPP during crystallization, which can improve toughness and heat distortion temperature of iPP while decrease its stiffness (Tordjeman et al., 2001; Zhao et al., 2008). Thereby, it is well expected to balance the iPP's stiffness and toughness. Xin's research group firstly proposed the idea of compounding α/β NAs. However, whether compounding α, β NAs will enhance stiffness and toughness simultaneously or not and what influence will α/β compounded NAs take on the crystallization kinetics, crystallization morphologies, and mechanical

different properties like optical and mechanical properties.

proprieties of iPP call our eye.

**1. Introduction** 

Witze, A. (2010). Building a cheaper catalyst*. Science News* Web Edition. http://www.sciencenews.org/view/generic/id/57618/title/Building\_a\_cheaper\_ catalyst
