Principles of Mössbauer Spectroscopy

262 Pages·1976·9.704 MB·English

by  T. C. Gibb (auth.)

STUDIES IN CHEMICAL PHYSICS
General Editor
A.D. Buckingham F.R.S., Professor of Chemistry,
University of Cambridge
Series Foreword
The field of science known as 'Chemical Physics' has
greatly expanded in recent years. It is an essential part
of both physics and chemistry and now impinges on
biology, crystallography, the science of materials and
even on astronomy. The aim of this series is to present
short, authoritative and readable books on different
topics in chemical physics at a level that is appreciated
by the non-specialist and yet is of prime interest to the
expert-in fact, the type of book that we all welcome
and enjoy.
I was grateful to be given the opportunity to help
plan this series, and warmly thank the authors and
publishers whose efforts have brought it into being.
A.D. Buckingham,
University Chemical Laboratory,
Cambridge, U.K.
Other titles in the series
Advanced Molecular Quantum Mechanics, R.E. Moss
Chemical Applications of Molecular Beam Scattering,
M.A.D. Fluendy and K.P. Lawley
Electronic Transitions and the High Pressure Chemistry
and Physics of Solids, H.G. Drickamer and C.W. Frank
Aqueous Dielectrics, J.B. Hasted
Statistical Thermodynamics, B.J.M. McClelland
Principles of
Mossbauer Spectroscopy
T.e. GIBB
Department of Inorganic and Structural Chemistry,
University of Leeds
SPRINGER-SCIENCE+BUSINESS MEDIA, B.V.
© T. C. Gibb 1976
Originally published by chapman and hall in 1976
Soficover reprint oft he hardcover 1st edition 1976
Typeset by Mid-County Press
and printed in Great Britain by
Fletcher & Son Ltd, Norwich
ISBN 978-0-412-13960-4 ISBN 978-1-4899-3023-1 (eBook)
DOI 10.1007/978-1-4899-3023-1
All rights reserved. No part of
this book may be reprinted, or reproduced
or utilized in any form or by any electronic,
mechanical or other means, now known or hereafter
invented, including photocopying and recording,
or in any information storage or retrieval
system, without permission in writing
from the publisher
Preface
The emergence of M6ssbauer spectroscopy as an important experi
mental technique for the study of solids has resulted in a wide range
of applications in chemistry, physics, metallurgy and biophysics.
This book is intended to summarize the elementary principles of
the technique at a level appropriate to the advanced student or
experienced chemist requiring a moderately comprehensive but
basically non-mathematical introduction. Thus the major part of
the book is concerned with the practical applications of Mossbauer
spectroscopy, using carefully selected examples to illustrate the
concepts. The references cited and the bibliography are intended
to provide a bridge to the main literature for those who subseouent
ly require a deeper knowledge.
The text is complementary to the longer research monograph,
'Mossbauer Spectroscopy', which was written a few years ago in
co-authorship with Professor N.N. Greenwood, and to whom I am
deeply indebted for reading the preliminary draft of the present
volume. I also wish to thank my many colleagues over the past
ten years, and in particular Dr. R. Greatrex, for the many stimu
lating discussions which we have had together. However my
greatest debt is to my wife, who not only had to tolerate my eccen
tricities during the gestation period, but being a chemist herself
was also able to provide much useful criticism of the penultirna te
draft.
Leeds, May 1975 T.e. Gibb
Contents
Preface
1 The Mossbauer Effect 1
1.1 Resonant absorption and fluorescence 2
1.2 The Mossbauer effect 5
1.3 The Mossbauer spectrum 9
1.4 The Mossbauer spectrometer 13
1.5 Mossbauer isotopes 16
1.6 Computation of data 19
References 21
2 Hyperfine Interactions 22
2.1 The chemical isomer shift 23
2.2 Magnetic hyperfine interactions 28
2.3 Electric quadrupole interactions 30
2.4 Combined magnetic and quadrupole interactions 36
2.5 Relative line intensities 38
References 43
3 Molecular Structure 45
3.1 Iron carbonyls and derivatives 46
3.2 Geometrical isomerism in Fe and Sn compounds 54
3.3 Linkage isomerism in cyano-complexes of Fe 56
3.4 Conformations in organometallic compounds of Fe 60
Contents
3.5 Stereochemistry in tin compounds 63
3.6 Molecular iodine compounds 67
Appendix Quadrupole splitting in cis- and trans-isomers 69
References 71
4 Electronic Structure and Bonding:
Diamagnetic Compounds 73
4.1 Formal oxidation state 74
4.2 Iodine 77
4.3 Tellurium and antimony 84
4.4 Tin 86
4.5 Covalent iron compounds 93
References 100
5 Electronic Structure and Bonding:
Paramagnetic Compounds 102
5.1 Quadrupole interactions 102
5.2 Magnetic hyperfine interactions 109
5.3 Spin cross-over 118
5.4 Pressure effects 121
5.5 Second and third row transition elements 124
5.6 Lanthanides and actinides 129
References 133
6 Dynamic Effects 135
6.1 Second-order Doppler shift and recoilless fraction 135
6.2 The Goldanskii-Karyagin effect 143
6.3 Electron hopping and atomic diffusion 145
6.4 Paramagnetic relaxation 148
6.5 Superparamagnetism 156
References 157
7 Oxides and Related Systems 159
7.1 Stoichiometric spinels 160
7.2 Non-stoichiometric spinels 165
7.3 Exchange interactions in spinels 168
7.4 Rare-earth iron garnets 174
7.5 Transferred hyperfine interactions 179
References 181
Principles ofM ossbauer Spectroscopy
8 Alloys and Intermeiallic Compounds 182
8.1 Disordered alloys 183
8.2 Intermetallic compounds 188
References 196
9 Analytical Applications 197
9.1 Chemical analysis 197
9.2 Silicate minerals 201
9.3 Surface chemistry 206
References 212
10 Impurity and Decay After-effect Studies 213
10.1 Impurity doping 214
10.2 Decay after-effects 221
References 232
11 Biological Systems 234
11.1 Haemoproteins 236
11.2 Ferredoxins 241
References 244
Bibliography 245
Observed Mossbauer Resonances 247
Index 248
CHAPTER ONE
The Mossbauer Effect
The study of recoilless nuclear resonant absorption or fluorescence
is more commonly known as Mossbauer spectroscopy. From its
first origins in 1957, it has grown rapidly to become one of the
most important research methods in solid-state physics and
chemistry.
Resonant nuclear processes had been looked for without success
for nearly thirty years before R.L. Mossbauer made his first acci
dental observation of recoilless resonant absorption in 191Ir in
1957 [1]. He not only produced a theoretical explanation of the
effect which now bears his name, but also devised an elegant ex
periment which today remains almost unmodified as the primary
technique of Mossbauer spectroscopy.
The Mossbauer effect is of fundamental importance in that it
provides a means of measuring some of the comparatively weak
interactions between the nucleus and the surrounding electrons.
Although the effect is only observed in the solid state, it is precise
ly in this area that some of the most exciting advances in chemi
stry and physics are being made. Because it is specific to a parti
cular atomic nucleus, such problems as the electronic structure of
impurity atoms in alloys, the after-effects of nuclear decay, and
the nature of the active-centres in iron-bearing proteins are just a
few of the diverse and many applications.
2 Principles of Mdssbauer Spectroscopy
1.1 Resonant absorption and fluorescence
Before delving into the details of the subject, it is worthwhile con
sidering the historical perspective of what has come to be consider
ed as a discovery of prime importance.
Atomic resonant fluorescence was predicted and discovered just
after the turn of the century, and within a few years the under
lying theory had been developed. From a simplified viewpoint, an
atom in an excited electronic state can decay to its ground state
by the emission of a photon to carry off the excess energy. This
photon can then be absorbed by a second atom of the same kind
by electronic excitation. Subsequent de-excitation re-emits the
photon, but not necessarily in the initial direction so that scat
tering or resonant fluorescence occurs. Thus if the monochromatic
yellow light from a sodium lamp is collimated and passed through
a glass vessel containing sodium vapour, one would expect to see a
yellow glow as the incident beam is scattered by resonant fluore
scence.
A close parallel can be drawn between atomic and nuclear reso
nant absorption. The primary decay of the majority of radioactive
nuclides produces a daughter nucleus which is in a highly excited
state. The latter then de-excites by emitting a series of r-ray pho
tons until by one or more routes, depending on the complexity
of the 'Y-cascade, it reaches a stable ground state. This is clearly
analogous to electronic de-excitation, the main difference being in
the much higher energies involved in nuclear transitions. It was
recognized in the 1920's that it should be possible to use the 'Y-ray
emitted during a transition to a nuclear ground-state to excite a
second stable nucleus of the same isotope, thus giving rise to nuc
lear resonant absorption and fluorescence.
The first experiments to detect these resonant processes by
Kuhn in 1929 [2] were a failure, although it was already recog
nized that the nuclear recoil and Doppler broadening effects (to
be discussed shortly) were probably responsible. Continuing
attempts to observe nuclear resonant absorption [3] were inspired
by the realization that the emitted 'Y-rays should be an unusually
good source of monochromatic radiation. This can easily be
shown from the Heisenberg uncertainty principle. The ground
state of the nucleus has an infinite lifetime and therefore there is
no uncertainty in its energy. The uncertainty in the lifetime of