Contents

Cover

Endorsments

Title Page

Copyright Page

Dedication

Preface

Chemistry – Solid State Chemistry – Materials Chemistry – Materials Science and Engineering

Materials chemistry

Materials science

Companion Website

Crystal Structure Library

Biography

1: Crystal Structures and Crystal Chemistry

1.1 Unit Cells and Crystal Systems

1.2 Symmetry

1.3 Symmetry and Choice of Unit Cell

1.4 Lattice, Bravais Lattice

1.5 Lattice Planes and Miller Indices

1.6 Indices of Directions

1.7 d-Spacing Formulae

1.8 Crystal Densities and Unit Cell Contents

1.9 Description of Crystal Structures

1.10 Close Packed Structures – Cubic and Hexagonal Close Packing

1.11 Relationship between Cubic Close Packed and Face Centred Cubic

1.12 Hexagonal Unit Cell and Close Packing

1.13 Density of Close Packed Structures

1.14 Unit Cell Projections and Atomic Coordinates

1.15 Materials That Can Be Described as Close Packed

1.16 Structures Built of Space-Filling Polyhedra

1.17 Some Important Structure Types

2: Crystal Defects, Non-Stoichiometry and Solid Solutions

2.1 Perfect and Imperfect Crystals

2.2 Types of Defect: Point Defects

2.3 Solid Solutions

2.4 Extended Defects

2.5 Dislocations and Mechanical Properties of Solids

3: Bonding in Solids

3.1 Overview: Ionic, Covalent, Metallic, van der Waals and Hydrogen Bonding in Solids

3.2 Ionic Bonding

3.3 Covalent Bonding

3.4 Metallic Bonding and Band Theory

3.5 Bands or Bonds: a Final Comment

4: Synthesis, Processing and Fabrication Methods

4.1 General Observations

4.2 Solid State Reaction or Shake ’n Bake Methods

4.3 Low Temperature or Chimie Douce Methods

4.4 Gas-Phase Methods

4.5 High-Pressure Methods

4.6 Crystal Growth

5: Crystallography and Diffraction Techniques

5.1 General Comments: Molecular and Non-Molecular Solids

5.2 Characterisation of Solids

5.3 X-Ray Diffraction

5.4 Electron Diffraction

5.5 Neutron Diffraction

6: Other Techniques: Microscopy, Spectroscopy, Thermal Analysis

6.1 Diffraction and Microscopic Techniques: What Do They Have in Common?

6.2 Optical and Electron Microscopy Techniques

6.3 Spectroscopic Techniques

6.4 Thermal Analysis (TA)

6.5 Strategy to Identify, Analyse and Characterise ‘Unknown’ Solids

7: Phase Diagrams and their Interpretation

7.1 The Phase Rule, the Condensed Phase Rule and Some Definitions

7.2 One-Component Systems

7.3 Two-Component Condensed Systems

7.4 Some Tips and Guidelines for Constructing Binary Phase Diagrams

8: Electrical Properties

8.1 Survey of Electrical Properties and Electrical Materials

8.2 Metallic Conductivity

8.3 Superconductivity

8.4 Semiconductivity

8.5 Ionic Conductivity

8.6 Dielectric Materials

8.7 Ferroelectrics

8.8 Pyroelectrics

8.9 Piezoelectrics

8.10 Applications of Ferro-, Pyro- and Piezoelectrics

9: Magnetic Properties

9.1 Physical Properties

9.2 Magnetic Materials, their Structures and Properties

9.3 Applications: Structure–Property Relations

9.4 Recent Developments

10: Optical Properties: Luminescence and Lasers

10.1 Visible Light and the Electromagnetic Spectrum

10.2 Sources of Light, Thermal Sources, Black Body Radiation and Electronic Transitions

10.3 Scattering Processes: Reflection, Diffraction and Interference

10.4 Luminescence and Phosphors

10.5 Configurational Coordinate Model

10.6 Some Phosphor Materials

10.7 Anti-Stokes Phosphors

10.8 Stimulated Emission, Amplification of Light and Lasers

10.9 Photodetectors

10.10 Fibre-Optics

10.11 Solar Cells

Further Reading

Appendix A: Interplanar Spacings and Unit Cell Volumes

Appendix B: Model Building

Equipment Needed

Sphere Packing Arrangements

Appendix C: Geometrical Considerations in Crystal Chemistry

Notes on the Geometry of Tetrahedra and Octahedra

Appendix D: How to Recognise Close Packed (Eutactic) Structures

Appendix E: Positive and Negative Atomic Coordinates

Appendix F: The Elements and Some of Their Properties

Questions

Index

This edition first published 2014
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Library of Congress Cataloging-in-Publication Data

West, Anthony R.
   Solid state chemistry and its applications / Anthony R. West. – Second edition, student edition.
      pages cm
   Includes index.
   ISBN 978-1-119-94294-8 (pbk.)
  1. Solid state chemistry. I. Title.
   QD478.W47 2014
   541′.0421–dc23
2013029528

A catalogue record for this book is available from the British Library.

ISBN: 9781119942948

Cover images created using CrystalMaker® software. CrystalMaker Software Ltd, www.crystalmaker.com

For Sheena, Isla, Graeme, Jenny and Susie

Preface

This book is a slimmed down, student edition of ‘Solid State Chemistry and its Applications’ whose second edition is scheduled for publication in 2015/6. It is modelled on the authors’ ‘Basic Solid State Chemistry’, but has been completely rewritten with about 40% new material added and all the diagrams drawn professionally, in full colour. The nine chapters in ‘Basic’ have become ten in this new edition since ‘Magnetic and Optical Properties’ is split into separate chapters.

In the period since the second edition of ‘Basic’ was published in 1999, we have witnessed many major new discoveries and developments in the solid state chemistry of inorganic materials with topics such as colossal magnetoresistance, multiferroics, light emitting diodes and graphene. New materials synthesis techniques have evolved such as mechanosynthesis, microwave-hydrothermal synthesis and atomic layer deposition and of course, there have been many improvements in the techniques used to characterise solids including use of synchrotrons for diffraction and spectroscopy as well as high resolution scanning transmission electron microscopy permitting atomic-level identification and structural imaging. It was felt that an updated version of both ‘Basic’ and ‘Solid State Chemistry and its Applications’ was long overdue, therefore.

A major feature of this new edition is the extensive coverage of the crystal structures of important families of inorganic solids. Purchasers of the book will be able to download, free, a bespoke and easy-to-use CrystalMaker® viewer program. The CrystalViewer software is accompanied by more than 100 crystal structure models which users will be able to view on their computers with the facility to rotate the structures, view them from different orientations and either highlight or hide different structural features. CrystalViewer and the accompanying structure files can be downloaded from the companion website at http://www.wiley.com/go/west/solidstatechemistrystudent.

Many people have helped and encouraged me in preparing this new edition. Special thanks are due to: John McCallum who produced many of the crystal structure drawings and files, Frances Kirk who prepared the whole manuscript, in electronic format, and Wiley staff Sarah Hall and Sarah Tilley for their enthusiastic encouragement and involvement: in particular, Sarah Hall was instrumental in making the CrystalMaker® arrangements and Sarah Tilley oversaw all the artwork preparations.

Anthony R. West

Sheffield

July 2013

Chemistry – Solid State Chemistry – Materials Chemistry – Materials Science and Engineering

Chemistry is an evolving subject! Traditionally, there have been three branches of chemistry: organic, physical and inorganic, with some arguments in favour of including analytical as a fourth branch. An alternative, fairly new classification (favoured by the author!) divides chemistry into two broad areas: molecular (which includes liquids and gases) and non-molecular (or solid state). The ways in which we think about, make, analyse and use molecular and non-molecular substances are completely different, as shown by a comparison of one ‘simple’ substance in each category, toluene and aluminium oxide:

Comparison of the chemistries of molecular and non-molecular materials

Thus, for toluene, once its formula and molecular structure had been determined there were few remaining issues to be resolved other than, perhaps, the detailed packing arrangement of molecules in crystalline toluene at low temperatures or the possible discovery and evaluation, even today, of as-yet unknown chemical, biological or pharmaceutical properties of pure toluene.

Alumina, by contrast, is a highly complex material; its properties, and therefore potential applications, depend on different aspects of its structure (bulk, defect, surface, nano), the methods needed to fabricate it in different forms and shapes, the possibility of doping to modify its properties and the characterisation or determination of its structure (and its composition, whether homogeneous or heterogeneous, if doped) across all length scales. This is solid state chemistry!

The biggest contrast between molecular and non-molecular materials is that the latter can be doped, allowing modification and control of properties such as magnetism, superconductivity and colour/optical band gap. By contrast, attempts to dope molecules are inevitably frustrated since replacing one atom in the molecule by another, or creating defects such as missing atoms, lead to entirely different molecules.

In recent decades, materials chemistry has emerged as a distinct branch of chemistry which covers both non-molecular, solid state materials (oxides, halides, etc.) and many molecular materials (especially, functional polymers and organic solids with potentially useful physical properties). Materials chemistry cuts across the traditional disciplines of chemistry but also includes something extra which is an interest in the physical properties of compounds and materials. In the past, solid state physics and materials science have been the usual ‘home’ for physical properties; but now, they are an intrinsic part of solid state and materials chemistry.

The distinction between materials chemistry and materials science is often unclear but can be summarised broadly as follows:

Materials chemistry

Synthesis – structure determination – physical properties – new materials

Materials science

Processing and fabrication – characterisation – optimisation of properties and testing – improved/new materials for engineering applications in products or devices.

Materials science focuses on materials that are already known to be useful or have the potential to be developed for applications, either by compositional control to optimise properties or by fabrication into desired forms, shapes or products. Materials science therefore includes whatever aspects of chemistry, physics and engineering that are necessary to achieve the desired aims.

Materials chemistry is much more than just a subset of materials science, however, since it is freed from the constraint of a focus on specific applications; materials chemists love to synthesise new materials and measure their properties, some of which may turn out to be useful and contribute to the development of new industries, but they do this within an overarching interest in new chemistry, new structures and improved understanding of structure – composition – property relationships.

A curious fact is that, in the early days of chemistry, inorganic chemistry had as its main focus, the elements of the periodic table and their naturally occurring or easy-to-make compounds such as oxides and halides. Inorganic chemistry subsequently diversified to include organometallic chemistry and coordination chemistry but interestingly, many traditional inorganic materials have returned to centre-stage and are now at the heart of solid state materials science. Examples include: Cr-doped Al2O3 for lasers; doped Si semiconductors for microelectronics; doped ZrO2 as the solid electrolyte in solid oxide fuel cells; BaTiO3 as the basis of the capacitor industry with a total annual production worldwide exceeding 1012 units; copper oxide-based materials for superconductor applications; and many, many more. The scope for developing new solid state materials/applications is infinite, judging by the ‘simple’ example of Al2O3 described above. Most such materials tend not to suffer from problems such as volatilisation, degradation and atmospheric attack, which are often a drawback of molecular materials, and can be used safely in the environment.

It is important to recognise also that physical properties of inorganic solids often depend on structure at different length scales, as shown by the following examples:

Thus in the case of ruby, which is a natural gemstone and was the first material in which LASER action – light amplification by stimulated emission of radiation – was demonstrated, two structural aspects are important. One is the host crystal structure of corundum, α-Al2O3 and the other is the Cr3+ dopant which substitutes at random for about 1% of the Al3+ ions in the corundum lattice: the Cr-O bond lengths and the octahedral site symmetry are controlled by the host structure; the two together combine to give the red ruby colour by means of d–d transitions within the Cr chromophore and the possibility of accessing the long-lived excited states that are necessary for LASER action.

A remarkable example of the effect of crystal structure details at the unit cell scale on properties is shown by dicalcium silicate, Ca2SiO4 which is readily prepared in two polymorphic forms at room temperature. One, the β-polymorph, reacts with water to give a semicrystalline calcium silicate hydrate which sets rock-solid and is a main constituent of concrete; the other polymorph, γ-Ca2SiO4, does not react with water. Just think, the entire construction industry rests on the detailed polymorphism of dicalcium silicate! It is not sufficient that one of the key components of cement has the right composition, Ca2SiO4; in addition, the precise manner in which ions are packed together in the solid state is critical to its hydration properties and whether or not it turns into concrete.

At the nanoscale, crystalline particles may contain many hundreds of unit cells but often their properties are different from powders, ceramics or single crystals of the same material with larger-sized grains simply because of the influence of surface energies. In small nanoparticles, surface free energies and structures increasingly dominate the total free energy of a material, as shown by the colour, and associated band gap, of CdS nanoparticles (or colloids in older terminology) which can be fine-tuned by controlling the particle size.

Some properties are determined by structure at the micron (1 μm = 103 nm = 104 Å = 10−3 mm) scale and this is the reason why ‘microstructure’ features strongly in the characterisation of metals and ceramics, primarily using optical and electron microscopy techniques. Frequently, impurities/dopants may precipitate at grain boundaries and surfaces and these can have a dramatic influence on for instance, the mechanical properties.

These examples illustrate the awesome challenges that must be met before an inorganic solid can be regarded as fully characterised across the length scales. This, coupled with the enormous number of inorganic crystal structures that are known, and the possibility to introduce dopants which modify properties, underlines why solid state chemistry is a central subject to many areas of physical science, engineering and technology.

This book concerns solid state chemistry and focuses on inorganic solids: their crystal structures, defect structures and bonding; the methods used to synthesise them and determine their structures; their physical properties and applications. Organic and other molecular materials are included in the coverage if their properties in the solid state complement, or relate to, those of inorganic solids. Physical properties are an intrinsic part of solid state chemistry since the whole area of structure–property relations requires the insights and input of chemistry to synthesise and characterise materials, as well as a good understanding of physical properties and the factors that control them.

Companion Website

This textbook is supported by a website which contains a variety of supplementary resources:

http://www.wiley.com/go/west/solidstatechemistrystudent

Online you will find PowerPoint slides of all figures from the book, as well as solutions to the set of questions. The website also gives you access to a CrystalMaker® viewer program. The CrystalViewer software is available for Windows and Mac, and is accompanied by a broad array of crystal structures for you to view and manipulate.

Crystal Structure Library

A Crystal Structure Library is available on the companion website containing >100 structures which can be examined in detail using the CrystalViewer Software. The structures which correspond directly to figures in the book are listed below, with the relevant figure number noted in parentheses. Many more crystal structures are available online, including minerals and other inorganic structures. Further structures may be added from time to time.

Major Inorganic Structure Types (and relevant book diagrams)

Biography

Tony West obtained his BSc degree in Chemistry at University College Swansea and his PhD at the University of Aberdeen, where he worked with Professor F. P. Glasser on silicate chemistry. He was appointed as a Lecturer in Aberdeen in 1971 and developed a lifetime interest in the then-emerging field of solid state chemistry with special interest in the synthesis of new oxide materials, their crystal structures and electrical properties. He was awarded a DSc from Aberdeen in 1984 and rose through the ranks to become Professor of Chemistry in 1989 before moving to the University of Sheffield, Department of Materials Science and Engineering, as Head of Department in 1999, a post he held until 2007.

Tony was founding editor of the Journal of Materials Chemistry and subsequently established the Materials Chemistry Forum, which has now become the Materials Chemistry Division of the Royal Society of Chemistry. He organised the First International Conference on Materials Chemistry, MCI, in Aberdeen, 1993, and co-organised the first Materials Discussion, MDI, in Bordeaux, 1998. He also served as President of the Inorganic Chemistry Division of IUPAC, 2004–2007.

Tony is a Fellow of the Royal Society of Chemistry, the Institute of Physics, the Institute of Materials, Minerals and Mining (IOM3), and the Royal Society of Edinburgh. Over the years he has received several awards, including an Industrial Award in Solid State Chemistry from the RSC (1996), the Griffiths Medal and Prize from the IOM3 (2008), the Epsilon de Oro Award from the Spanish Society of Glass and Ceramics (2007) and the Chemical Record Lectureship from the Chemical Societies of Japan (2007). He has been awarded the 2013 John B. Goodenough Award in Materials Chemistry by the RSC, a lifetime award which recognises exceptional and sustained contributions to the field of materials chemistry.