This chapter discusses the application and interpretation of powder X-ray diffraction data. The form of the powder X-ray diffraction data obtained from a material will depend upon the crystal structure it adopts. This structure is delineated by the lattice type, crystal class, unit cell parameters, and the distribution of the various ion and molecule types within the unit cell. As a result of the enormous range of different structures which materials adopt, nearly all crystalline solids have a unique powder X-ray diffraction pattern in terms of the positions of the observed reflections and the peak intensities. In mixtures of compounds, each crystalline phase present will contribute its own unique set of lines to the powder diffraction pattern.
Application and interpretation of powder X-ray diffraction data
This chapter provides a background of crystallography. The structures of inorganic materials, the majority of which are crystalline in the solid state, are a key feature in the control of their chemistry and physical properties. The techniques used to identify and investigate such materials involve characterization of the bulk structure. The chapter begins by looking at crystal systems and unit cells; fractional atomic coordinates and projections; lattices; Bravais lattices; and lattice lines and planes, which are labelled using the Miller indices. It then explains X-ray diffraction. The scattering of X-rays from crystalline solids can be demonstrated by consideration of the diffraction from points on a set of lattice planes. Finally, the chapter details the powder technique, outlining the different methods of obtaining powder X-ray diffraction data.
Electronic, magnetic and optical properties of inorganic materials
This chapter focuses on the electronic, magnetic, and optical properties of inorganic materials. The electronic properties exhibited by solids are crucial in a large number of inorganic materials applications. These unique electronic properties result from the extended structures adopted by many inorganic materials, where strong interactions between the atoms, ions, or molecules occur throughout the lattice. In terms of conductivity, behaviour ranges from insulating through semiconducting to metallic and superconducting. Similarly, the interaction between the unpaired electrons in inorganic material structures gives rise to magnetic properties characteristic of the whole solid rather than the individual atoms. Finally, the potential for concerted ion displacements in neighbouring unit cells produces ferroelectrics and optoelectric materials. The chapter also considers the band theory.
Mark T. Weller
Inorganic Materials Chemistry begins by stating that the chemistry of solid inorganic materials has become a central theme in research and in the teaching of chemistry. This area is, however, often not given enough attention. Topics in this text include transition metal oxides, non-stoichiometry, zeolites, layer compounds chemistry, high temperature superconductors, and fullerides. In addition, the synthesis of these compound types is presented. As well as introducing and describing important solid-state materials, the text addresses the major experimental technique used to study and characterize the powder x-ray diffraction. The basis of this method and associated relevant crystallography is discussed; experimental data from this technique is used to illustrate topics throughout the text. This tying together of an experimental method and the chemistry is a useful approach to adopt.
This chapter assesses non-stoichiometry. Non-stoichiometric materials are characterized by two criteria. From a thermodynamic standpoint, the free energy of the system depends upon both the composition and temperature. A more useful criterion, in that the behaviour is readily identified by experiment, is that the lattice parameter of the system varies smoothly as a function of composition. All crystalline materials contain a certain number of defects. The chapter then looks at two types of defect which are commonly found in ionic inorganic compounds: Schottky defects and Frenkel defects. It also considers four non-stoichiometric systems which illustrate the major ways in which large compositional variations can be incorporated into materials through defects and interstitials. Finally, the chapter discusses the elimination of defects through the process of crystallographic shear, before examining intercalation compounds.
Some recent developments in inorganic materials chemistry
This chapter explores some recent developments in inorganic materials chemistry. Many of these have come in the area of new materials. The chemistry of high temperature superconducting phases, in terms of the synthesis and structure of these compounds, lies within the area of this text. More recently, the structural chemistry of C60 in its ionic compounds is also relevant, though the chemistry of this species is developing rapidly in many areas. Consideration of several superconducting systems shows two features in common. They all contain planes of the stoichiometry CuO2 formed by linking CuO4 square planes at all vertices, and they all have an average copper oxidation state in excess of 2+. The chapter then looks at the structural chemistry of fullerenes and fullerides.
The synthesis of inorganic materials
This chapter examines the synthesis of inorganic materials. The synthesis methods used in the preparation of inorganic materials, many of which have extended lattices rather than discrete molecules, are quite different from those used by organic, organometallic, and coordination chemists. Rather than altering a single functional group or ligand attached to a molecule, the materials chemist works with complete lattices, either building or modifying them. The chapter begins by looking at high temperature reactions. The most widely used method for the synthesis of inorganic materials follows an almost universal route that involves heating the components together at high temperature over an extended period. The chapter then details the process of the reaction between solids, before studying the precursor, solution, and gel methods. It also assesses hydrothermal methods, phase diagrams, and low temperature methods.
Transition metal oxides
This chapter evaluates transition metal oxides, reviewing binary transition metal oxide structures. The structure of many binary oxides can be predicted on the basis of the relative sizes of the metal and oxide ions and filling of holes in a close peaked oxide lattice. Such predictions of structure are more difficult for ternary phases. The combination of two or more metals in an oxide generates a wealth of structural possibilities dependent on the relative sizes of the two metal ions and the oxide ion. In addition, the stoichiometry of the ternary oxide may be changed by varying the proportions of the two component oxides and, for transition and lanthanide elements, the oxidation state. The chapter then looks at the perovskite structure, insertion compounds, lithium niobate, the spinel structure, and the K2NiF4 structure.
Zeolites, intercalation in layer materials and solid electrolytes
This chapter presents some widely studied inorganic materials which have significant applications and properties, including zeolites, intercalation in layer materials, and solid electrolytes. The zeolites are a group of compounds, many of which are naturally occurring minerals, named after their property of evolving water when heated. These materials are widely used for their ion exchange, absorption, and catalytic properties. The chapter then looks at two-dimensional intercalation chemistry, before considering fast ion conduction in solids. The diffusion of ions through solids is facilitated by the presence of suitable vacant sites to which a diffusing ion may migrate. In some materials, the presence of a large number of suitable sites within the structure for ion migration, even at low temperatures, allows facile diffusion of ions and these materials are known as fast ion conductors.