Solid State Chemistry and its Applications

Anthony R. West

• Publisher: Wiley
• Year: 2014
• ISBN:
  9781118676257
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Physical & Theoretical Chemistry

Solid State Chemistry and its Applications, 2nd Edition: Student Edition is an extensive update and sequel to the bestselling textbook Basic Solid State Chemistry, the classic text for undergraduate teaching in solid state chemistry worldwide.

Solid state chemistry lies at the heart of many significant scientific advances from recent decades, including the discovery of high-temperature superconductors, new forms of carbon and countless other developments in the synthesis, characterisation and applications of inorganic materials. Looking forward, solid state chemistry will be crucial for the development of new functional materials in areas such as energy, catalysis and electronic materials.

This revised edition of Basic Solid State Chemistry has been completely rewritten and expanded to present an up-to-date account of the essential topics and recent developments in this exciting field of inorganic chemistry. Each section commences with a gentle introduction, covering basic principles, progressing seamlessly to a more advanced level in order to present a comprehensive overview of the subject.

This new Student Edition includes the following updates and new features:

• Expanded coverage of bonding in solids, including a new section on covalent bonding and more extensive treatment of metallic bonding.
• Synthetic methods are covered extensively and new topics include microwave synthesis, combinatorial synthesis, mechano-synthesis, atomic layer deposition and spray pyrolysis.
• Revised coverage of electrical, magnetic and optical properties, with additional material on semiconductors, giant and colossal magnetoresistance, multiferroics, LEDs, fibre optics and solar cells, lasers, graphene and quasicrystals.
• Extended chapters on crystal defects and characterisation techniques.
• Published in full colour to aid comprehension.
• Extensive coverage of crystal structures for important families of inorganic solids is complemented by access to CrystalMaker® visualization software, allowing readers to view and rotate over 100 crystal structures in three dimensions.
• Solutions to exercises and supplementary lecture material are available online.

Solid State Chemistry and its Applications, 2nd Edition: Student Edition is a must-have textbook for any undergraduate or new research worker studying solid state chemistry.

1

Crystal Structures and Crystal Chemistry

Solid state chemistry is concerned mainly with crystalline inorganic materials, their synthesis, structures, properties and applications. A good place to begin is with crystal structures and crystal chemistry. All necessary crystal structure information is contained in data on unit cells, their dimensions and the positions or atomic coordinates of atoms inside the unit cell. Crystal chemistry combines this basic structural information with information about the elements, their principal oxidation states, ionic radii, coordination requirements and preferences for ionic/covalent/metallic bonding. A working knowledge of the Periodic Table and the properties of elements is, of course, invaluable to be able appreciate crystal chemistry, but conversely, knowledge of crystal structures and especially crystal chemistry provides a very useful way to gain increased understanding of the elements and their compounds.

Many of the properties and applications of crystalline inorganic materials revolve around a surprisingly small number of structure types. In this chapter, the main families of inorganic structures are reviewed, especially those which have interesting properties; more details of the vast array of structures may be found in the encyclopaedic text by Wells and also in the Wyckoff Crystal Structures book series. First, however, we must consider some basic concepts of crystallography.

1.1 Unit Cells and Crystal Systems

Crystals are built up of regular arrangements of atoms in three dimensions; these arrangements can be represented by a repeat unit or motif called the unit cell. The unit cell is defined as the smallest repeating unit which shows the full symmetry of the crystal structure. Let us see exactly what this means, first in two dimensions. A section through the NaCl structure is shown in Fig. 1.1(a); possible repeat units are given in (b) to (e). In each, the repeat unit is a square and adjacent squares share edges and corners. Adjacent squares are identical, as they must be by definition; thus, all the squares in (b) have Cl− ions at their corners and centres. The repeat units in (b), (c) and (d) are all of the same size and, in fact, differ only in their relative position. The choice of origin of the repeat unit is to some extent a matter of personal taste, even though its size, shape and orientation are fixed. The repeat unit of NaCl is usually chosen as (b) or (c) rather than (d) because it is easier to draw and visualise the structure as a whole if the repeat unit contains atoms or ions at special positions such as corners and edge centres. Another guideline is that usually the origin is chosen so that the symmetry of the structure is evident (next section).

Figure 1.1 (a) Section through the NaCl structure, showing (b) to (e) possible repeat units and (f) incorrect units.

In the hypothetical case that two-dimensional (2D) crystals of NaCl could form, the repeat unit shown in (e), or its equivalent with Cl at the corners and Na in the middle, would be the correct unit. Comparing (e) and, for example, (c), both repeat units are square and show the 2D symmetry of the structure; as the units in (e) are half the size of those in (c), (e) would be preferred according to the above definition of the unit cell. In three dimensions, however, the unit cell of NaCl is based on (b) or (c), rather than (e) because only they show the cubic symmetry of the structure (see later).

In (f) are shown two examples of what is not a repeat unit. The top part of the diagram contains isolated squares whose area is one-quarter of the squares in (c). It is true that each square in (f) is identical but it is not permissible to isolate unit cells or areas from each other, as happens here. The bottom part of the diagram contains units that are not identical; thus square 1 has Na in its top right corner whereas 2 has Cl in this position.

The unit cell of NaCl in three dimensions is shown in Fig. 1.2; it contains Na at the corner and face centre positions with Cl at the edge centres and body centre. Each face of the unit cell looks like the unit area shown in Fig. 1.1(c). As in the 2D case, the choice of origin is arbitrary; an equally valid unit cell could be chosen in which Na and Cl are interchanged. The unit cell of NaCl is cubic. The three edges: a, b and c are equal in length. The three angles: α (between b and c), β (between a and c) and γ (between a and b) are all 90°. A cubic unit cell also possesses certain symmetry elements, and these, together with the shape define the cubic unit cell.

Figure 1.2 Cubic unit cell of NaCl, a = b = c.

The seven crystal systems listed in Table 1.1 and shown in Fig. 1.3 are the seven independent unit cell shapes that are possible in three-dimensional (3D) crystal structures. Six of these unit cell shapes are closely inter-related and are either cubic or can be derived by distorting a cube in various ways, as shown in Fig. 1.3(b).

Table 1.1 The seven crystal systems

Figure 1.3 (a) The seven crystal systems and their unit cell shapes; (b) five of the seven crystal systems can be derived from cubic by structural distortions.

Thus, if one axis, c, is of different length to the others, the shape is tetragonal; if all three axes are different, the shape is orthorhombic. If, now, one of the angles, β, is not 90°, the shape is monoclinic, whereas if all three angles differ from 90°, the shape is triclinic. Finally, if the cube is stretched, or compressed, along a body diagonal so that all three angles remain equal, but different from 90°, the shape is trigonal.

The remaining unit cell shape is hexagonal. A hexagonal-shaped box is shown in Fig. ...