Structure and Properties of Inorganic Solids PDF
Preview Structure and Properties of Inorganic Solids
STRUCTURE AND PROPERTIES OF INORGANIC SOLIDS BY FRANCIS S. GALASSO United Aircraft Research Laboratories ILLUSTRATED BY W. DARBY PERGAMON PRESS Oxford · New York · Toronto Sydney · Braunschweig Pergamon Press Ltd., Headington Hill Hall, Oxford Pergamon Press Inc., Maxwell House, Fairview Park, Elmsford, New York 10523 Pergamon of Canada Ltd., 207 Queen's Quay West, Toronto 1 Pergamon Press (Aust.) Pty. Ltd., 19a Boundary Street, Rushcutters Bay, N.S.W. 2011, Australia Vieweg & Sohn GmbH, Burgplatz 1, Braunschweig Copyright © 1970 Pergamon Press Inc. All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of Pergamon Press Inc. First edition 1970 Library of Congress Catalog Card No. 70-104123 PRINTED IN GREAT BRITAIN BY PAGE BROS. (NORWICH) LTD. 08 006873 1 PREFACE THIS is an up-to-date reference book written to meet the needs of teachers of advanced undergraduate and graduate courses and of researchers in the various disciplines which make up the field of materials sciences. It describes the structure of metals, intermetallics, halides, hydrides, carbides, borides and other inorganic phases as well as some of their properties of current interest. This book was not intended to be as complete as such excellent and thorough texts as Structural Inorganic Chemistry by Alexander Wells and Crystal Structures, Vols. I, II and III, by Professor Ralph G. Wycoff, which deal primarily with structures. It is rather intended as mainly a survey of structures of those solids which have properties of considerable contemporary interest. Some of the structures and properties which fall into this category are Cu AlMn, spinel, magnetoplumbite and garnet structures (ferromagnetic 2 properties), fluorite and scheelite structures (laser properties), perovskite structure (ferroelectric properties), the ß-tungsten structure (superconducting properties) and the zinc blende structure (semiconducting properties). In order to simplify and systematize the presentation of structures, I divided them into related groups, describing the simple ones first, and using these in describing the more complex structures. By placing similar structures together, it is possible to visualize a number of them as simple variations of a common one. Several figures of each structure, always using the convention described in the introduction, are included with the descriptions. Because this book was written for readers with diverse backgrounds such as engineering, chemistry, metallurgy, physics, ceramics and mineralogy, I felt that background information on crystallography and properties should be presented in Chapter 1 to assist the readers who may need it to understand some of the data and topics covered in subsequent chapters. Each of these chapters begins with a brief description of the related structures. For each structure the name, a common compound with the structure, the structure type, the space group, and the symmetry are given. A simple description of the structure is presented with several figures, the atomic positions are listed for the reader with a knowledge of crystallography, unit cell data for phases with the structure are tabulated and a discussion of the properties of more im portant materials is given. For some structures physical constants of com pounds are tabulated. The properties of elemental solids are treated very briefly because they are generally well known. On the other hand, properties IX X PREFACE of compounds are considered in greater detail. The structure and properties of intermetallics, borides, carbides, halides, hydrides and oxides are discussed in the appropriate chapters and they are summarized in the last chapter. The properties of a number of other phases not covered in Chapters 1—12 are listed in the Appendix. I am grateful to those responsible for my writing this book and for their help in deciding what should be included. I became convinced that a book which emphasized structures and properties of materials of current interest and use would be of great value. Professor Martin Buerger influenced the decision to present these structures in a systematic manner and Professor Roman Smoluchowski suggested the emphasis on properties. I am grateful to members of the United Aircraft Research Laboratories for helping me prepare basic discussions of the properties found in the intro duction. These scientists are Drs. George Yntema and Fred Otter, Jr. (super conductivity), Mr. Frank Douglas (dielectric properties), Dr. Alexander Shuskus (magnetic properties), Dr. Michael Brienza (optical properties) and Drs. Earl Thompson, Robert Sierakowski and Kenneth Kreider (mechanical properties). I owe Dr. Gerry Peterson a special debt of gratitude for reviewing these discussions and I must thank Professor Lewis Katz of the University of Connecticut, Dr. Michael Kestigian of Sperry-Rand Research Laboratories and Dr. John Longo of Lincoln Laboratories for each reviewing several chapters. I thank my daughter, Cynthia, and Wilda Darby for their assistance in collecting the data, United Aircraft Research Laboratories personnel, Kathy Donahue, Joyce Hurlburt and Bonnie True and my wife, Lois, for preparing the manuscript and Nancy Letendre, Carol Begansky and Willie Jenkins for helping Wilda Darby with the illustrations. CHAPTER 1 INTRODUCTION THIS chapter provides an introductory treatment of crystallography and of material properties as background for those readers who may not be familiar with these topics. This simplifies the presentation of data and discussions in the following chapters. 1.1. Crystallography Lattice and Unit Cells The materials considered in this book are crystalline which means that atoms in each crystal are arranged in a three-dimensional periodic pattern in space. Starting at any point in the crystal and moving in any direction, points with the same environment as the original point will be found. These points will be evenly spaced apart along each particular direction. A three- dimensional set of such points obtained by using three non-coplanar direc tions originating from one point is called a Bravais lattice. All crystals are based on one of the fourteen Bravais lattices shown in Fig. 1.1a. The three directions and the repeat distance along each one of them deter mine a parallelepiped which reproduced indefinitely will fill out the space. These directions called crystalline axes are usually chosen to coincide with axes of high symmetry (see below) although this is not possible for the triclinic system and for two directions in the monoclinic system. The smallest parallele piped thus defined is called the unit cell. In the face-centered, body-centered and rhombohedral systems the preferred unit cell is larger than the minimum Bravais cell because the latter is more difficult to visualize and use. The unit cell has dimensions a, b and c and angles α, β and γ representing the angles between b and c, c and a, and a and b respectively. Table 1.1a presents data which are used to describe unit cells of various types. Symmetry Symmetry operations are essential in describing crystalline structures. In many instances, for example, only half the structure need be identified because the other half is its mirror image. Thus, it is said that there is a mirror plane between these halves. A unit cell is said to have a rc-fold rotation axis if a rotation of 360/n degrees around this axis brings it to an identical place in the cell. A tetragonal unit 1 2 STRUCTURE AND PROPERTIES OF INORGANIC SOLIDS cell is said to have a fourfold rotation axis perpendicular to one set of faces. A hexagonal unit cell has one sixfold rotation axis. Some of these symmetry operations are illustrated in Fig. 1.1b and the minimum symmetry for each system is given in Table 1.1a. Since symmetry operations are used only sparingly in this book, no further description will be given. Planes and Directions The orientation of a plane is given by its Miller index which is defined as the Simple cubic Simple tetragonal Body centered Face centered Body centered cubic cubic tetragonal Simple Base centered Body centered Face centered orthorhombic orthorhombic orthorhombic orthorhombic Rhombohedral Simple monoclinic Hexagonal Base centered Triclinic monoclinic FIG. 1.1a The Bravais lattices INTRODUCTION 3 TABLE 1.1a. Crystal Systems System Unit cell dimensions Lattice type Minimum symmetry Cubic = isometric a = b = c;a = ß = y = 90° P, I,F Four 3-fold rotation axes (four 3 or 3) Tetragonal a = b #c;a = ß = y = 90° P, I One 4-fold rotation (or rotation inversion) axis (4 or 4) Orthorhombic a ^b ^ c;a = β = y = 90° P, I, F, C Three perpendicular 2-fold rotation (or rotation inversion) axes(222 or 222) Monoclinic a = b # c;a = y = 90° φ β P, I One 2-fold rotation (or rotation- inversion) axis (2 or 2) Triclinic a^b^c;oL^ß^y P None Hexagonal a = b ^ c; a = ß = 90°, y = 120° P One 6-fold rotation (or rotation inversion) axis (6 or 6) Rhombohedral = b = c;a = jS = 7#90° P One 3-fold rotation a (or rotation inversion) axis (3 or 3) set of reciprocals of the fractional intercepts which the plane makes with the crystallographic axes. The intercepts have to be expressed in terms of the unit distances a, b and c along the three axes. In the cubic system the [hkl] direction is perpendicular to the (hkl) plane. Examples of some planes and directions are shown in Fig. 1.1c. Crystal Structure The atoms in a structure are present in space either on the points of a Bravais lattice or in some fixed relation to these points. The atomic positions are given in terms of fractions x, y, z of the unit cell edges a, b, c in directions parallel to these edges. In this book the origin of the unit cell is always taken at the bottom, back left-hand corner of cubic, tetragonal and orthorhombic cells and the back bottom corner of hexagonal cells. The values x, y and z are taken from the origin. When the number of atoms in a particular unit cell is being considered, it must be remembered that there are unit cells around it which may share some of the atoms. For example, an atom at the origin is at 0,0,0, but because this atom is shared by eight other unit cells, only one-eighth of the atom belongs to a single unit cell. Thus an atom in the face of a unit cell is also in 4 STRUCTURE AND PROPERTIES OF INORGANIC SOLIDS Mirror plane Rotation axis > Center of symmetry First operation of a four-fold rotation - inversion axis FIG. 1.1b Symmetry elements d(200) [100] :0 ^^Γ^ yJM SPIF ipi mi FIG. 1.1C Miller indices INTRODUCTION 5 the opposite face and an atom at an edge is also on three other edges. Examples are shown in Fig. l.ld. In this book the x, y and z values for each atom in the unit cell are given unless the number of atoms is very large. In trying to visualize structures from data for complex structures and for those presented in other books, there are several factors which should be noted. If a unit cell has a center of symmetry, then only half the atomic positions are sometimes given. The other atomic positions are obtained by changing the sign of each value o fx, y and FIG. l.ld Atomic positions 6 STRUCTURE AND PROPERTIES OF INORGANIC SOLIDS z. For example, if an atom is located at x, y, z, and another one at x ,j/, z, then these two positions can be written as + (x, y, z). Sometimes, x, y and z values will be given which are to be added to each x', yr and z' value listed below them. For example, if 0,0,0; ü, i is written above i, i J, this means that there are two atoms, one at i \, \ and the other at |, |, f. Since these positions (0, 0, 0; |, ^, i) are positions in a body-centered lattice, B.C. is sometimes written instead of the two positions or F.C. instead of (0,0,0; Ü, 0; j 0, \; 0, \, j) for positions in a face-centered lattice. 9 Another way of presenting the atomic positions is by giving the space group symbol or number and the letter for each group of equivalent positions. The letter and positions are listed in the International Tables for X-ray Crystallography, Vol. 1, The Kynock Press, Birmingham, England, 1952. Fundamental Configurations Within many structures groups of atoms form distinct configurations. Two of the most common configurations or polyhedra are the tetrahedron and the octahedron. A tetrahedral configuration of atoms is formed by placing three atoms close packed together in a triangle and then setting another atom on top (see Fig. Lie). If these atoms are large, the hole in the center can be FIG. Lie Tetrahedral arrangement of atoms of one element about the atom of another element occupied by a small atom. Such a tetrahedral hole is found in each corner of a face-centered cubic lattice. The hole is situated in the center of each octant of the cube. In this book this position is referred to as being in the corner of the cube as opposed to an atom at the corner, which is one of the apexes of the tetrahedra. An octahedral arrangement of atoms can be formed by placing four atoms in a square and setting one atom above and one below it (Fig. l.lf). The hole in this configuration is larger than the one in the tetrahedral arrangement of atoms and therefore must be filled by larger atoms. The coordination number, i.e. the number of nearest neighbor atoms within a tetrahedron is four, and it is six for an octahedron.
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