BOOK
REVIEWS
t o an u n d e r s t a n d i n g of ferroelectrics is b y a knowledge
of their structure, t h o u g h she points out t h a t this approach can be m a d e q u a n t i t a t i v e only w h e n considerably
more is known about the n a t u r e of covalent bonds.
I n short, this book will be found useful for its good
coverage of the structural properties a n d the various
theories of ferroelectrics b u t it does n o t contain, and its
a u t h o r did n o t i n t e n d it to contain, a comprehensive
record of the electrical properties.
A. G. CHYNOWETH
Bell Telephone Laboratories
Murray Hill, N.J., U.S.A.
Dislocations and Mechanical Properties of
Crystals. B y J. C. FtSHER, W. G. JOHnSTOn,
R. THOMSON a n d T. VREELAND, Jr. Pp. x i v + 6 3 4
w i t h m a n y figs. N e w Y o r k : W i l e y ; L o n d o n : Chapm a n a n d Hall. 1957. P r i c e £ 6.
This book consists of a series of papers (with discussion)
presented at a small I n t e r n a t i o n a l Conference on Dislocations a n d Mechanical Properties of Crystals held at
Lake Placid, on S e p t e m b e r 6 t h - 8 t h , 1956. The conference
was a t t e n d e d b y 41 experts in this field, a n d by limiting
t h e a t t e n d a n c e to such a small n u m b e r , it was possible
to have useful stimulating discussions. There is little
d o u b t t h a t small conferences of this t y p e are ideal for
interchange of information and ideas b e t w e e n experts.
The value of the conference is, however, e n h a n c e d enorm o u s l y by recording t h e proceedings, a n d so enabling
other research workers to become a c q u a i n t e d w i t h the
m o s t recent developments. The editors of this report are
to be congratulated on the v e r y fine book which t h e y
have produced, which will be of great value to every
research worker in this field.
The report is d i v i d e d into eight parts corresponding to
different subjects discussed at t h e conference. The first
p a r t deals w i t h m e t h o d s of direct observations of dislocations; studies are described in which dislocations are
observed by 'decoration', etching, or transmission electron
microscopy. These techniques of observation of individual
dislocations have helped to p u t dislocation t h e o r y on a
firm foundation. Many predictions of dislocation t h e o r y
have been confirmed.
The second part consists of papers on the deformation
of single crystals including a remarkable paper by Blewitt
a n d his colleagues on t w i n n i n g and low t e m p e r a t u r e
deformation in copper. The n e x t part, on w o r k - h a r d e n i n g
a n d recovery, contains a comprehensive review by Seeger
(85 pages) on glide a n d w o r k - h a r d e n i n g in f.c.c, a n d h.c.p.
metals. On reading this paper one feels t h a t whereas the
properties of isolated dislocations are u n d e r s t o o d a n d
have been confirmed in some detail, m u c h remains to be
done theoretically in relating the bulk mechanical properties to the behaviour of assemblies of dislocations, a n d
e x p e r i m e n t a l l y in testing those theories which have been
suggested. The paper by Boas on stored energy, resistivity, a n d density m e a s u r e m e n t s on cold-worked metals
underlines again the discrepancy b e t w e e n the observed
resistivity a n d t h a t calculated for u n e x t e n d e d dislocations. Seeger a t t r i b u t e s the discrepancy to stacking faults,
but a full theoretical t r e a t m e n t is still required on this
point.
A section on alloys includes a theoretical paper by
755
H. Susuki on the yield strength of binary alloys as well
as a n u m b e r of e x p e r i m e n t a l papers, in particular one on
t h e deformation of alloy single crystals by Garstone a n d
H o n e y c o m b e . I t appears t h a t more studies of this t y p e
are n e e d e d to elucidate the n a t u r e of h a r d e n i n g mechanisms in alloys.
The n e x t part includes a review of internal friction
p h e n o m e n a due to dislocations (Lficke a n d Granato);
this t e c h n i q u e is e x t r e m e l y sensitive to the presence of
dislocations and promises to be a powerful tool in t h e
s t u d y of dislocations. Two papers on fatigue underline
our lack of u n d e r s t a n d i n g of this p h e n o m e n o n .
The short section on dislocation t h e o r y includes an
i m p o r t a n t paper by Leibfried on t h e r m a l m o t i o n of
dislocation lines, which has applications to t h e problems
of t h e r m a l activation of dislocations at obstacles.
A few papers on whiskers are followed by a section on
radiation damage, including papers b y t h e U r b a n a a n d
Oak Ridge Schools on annealing. The detailed interp r e t a t i o n of t h e complicated annealing characteristics
a n d t h e precise n a t u r e of the d a m a g e are far from clear.
The n a t u r e of the papers presented at this conference
is characteristic of t h e present trends in this subject.
The theory of m a n y of the basic properties of dislocations
has been worked out, and it is clear t h a t 'Dislocation
Physics' is becoming an 'experimental' subject. I t is now
up to the experimentalists to test directly the predictions
of t h e o r y a n d to suggest new directions in which the
t h e o r y m i g h t be developed. On the other h a n d there is
p l e n t y of scope for the theorist in t h e s t u d y of the
properties of assemblies of dislocations a n d of bulk
properties of metals, as well as in the field of radiation
damage.
P. B. I-hRSCH
University of Cambridge
Department of Physics
Crystallographic Laboratory
Cavendish Laboratory
Cambridge, England
Splitting
of Terms
in Crystals. B y HANS A.
BETHE. Pp. 69. N e w Y o r k : C o n s u l t a n t s B u r e a u ,
Inc. N e w Y o r k 11. 1958. P r i c e $3.00.
I t is a t e s t i m o n y for the solid and informative work
published in this 1929 paper by H. B e t h e t h a t there is
now sufficient d e m a n d for an English translation to be
made. I n fact, in re-reading the paper after a long period,
one is all the m o r e impressed by the author's sovereign
application of group theory to the p r o b l e m of the splitting
of atomic levels caused by placing an a t o m in the electrical
field of crystallographic s y m m e t r y which is created by
the charges of the surrounding atoms. This predictable
effect prepares the way for the discussion of further
changes of the energy level scheme by electron exchange
between neighbours. The m a i n a d v a n c e m a d e recently
b e y o n d Bethe's t r e a t m e n t is the inclusion of spin interaction in the group theoretical t r e a t m e n t by F i e k
(Zs.f. Phys. 147, 1957, p. 307).
The translation is clear and adequate, a n d the price
moderate.
P. P. EWALD
Polytechnic Institute of Brooklyn
Brooklyn 1. N.Y., U.S.A.