temperature, because separation between the weak obstacles
lying on the dislocation is wider. In addition, it is supposedthat the decrease of Tpl is attributable to the loss of
tetragonality in Fleischer's model as I-V dipoles aggregate.Then, the force-distance profile between a dislocation and
aggregates for the annealed KCI:Sr2+ cannot be approximated by Flei.scher's model and the activation energy for the break-away of a di. slocation from weak obstacles becomes small for the annealedspecimen, compared with the quenched one. Furthermore, the
critical temperature, Tc, for the annealed KCI:Sr2+ is slightlysmaller in contrast to that for the quenched one.
Chapter 5. Summary
The strain-rate cycling test during the Blaha effect measurement can separate the effective stress due to a weak obstacle such as
an impurity, from that due to dislocation cutting. And the
relation between the strain-rate sensitivity and the stressdecrement, which is obtained from the measurement, provides information on the interaction between a dislocation and an impunty as described in the present studies. The conclusions of
this thesis are summarjzed as fo]lows.
(1)The plots of the strain-rate sensitivity and stress decrement for KCI doped with divalent cation impurities have two bending points and two plateau r'egions. The first bending poi-nt, Tpl, corresponds to the effective stress due to weak obstacles which
is the largest separation on the mobile dislocation.
(2)The temperature dependence of Tpl reveals the force-djtstance profile between a dislocation and obstacles, and the critical temper.ature Tc, which is given by the relation between Tl/2 and 1/2Tpl with respect to Fleischer's model, is 191, 221, 227, and
277K for Kcl:Mg2+, Kcl:ca2+, Kcl:sr2+, and Kcl:Ba2+,respectively.
(3)The activation energy for the interaction between a dislocation and I-V dipole is O.50, O.63, and O.71eV for
Kcl:ca2+, Kcl:sr2+, and Kcl:Ba2+, respectively. The results suggest the tetragonality Ae, resulting from the formation ofI-V dipole for alkali halide doped with divalent cation, in Fleischer's model increases when the divalent ionic size
approaches increasingly the K+ ion's.
(4)When I-V dipoles turn into the aggregates for KCI:Sr2+, the force-distance profile cannot be approximated to Fleischer's
model, and if the force-distance profile for the annealed
KCI:Sr2+ can be approximated to the triangle, the activation energy for the break-away of a dislocation from obstacles is small as compared with the quenched one. Furthermore, Tc for the annealed KCI:Sr2+ is slightly small in contrast to that for thequenched one.
Acknowledgements
The author is deeply indebted to Professor N.Takeuchi at Kanazawa
Universtty for his continuing assistance throughout this work.
The author would cordially like to acknowledge Associate professor T.Ohgaku for many useful suggestions and valuable discussion throughout this work and for his comments on the
m anuscnpt.
The author acknowledges all members of the laboratories for
their kind help.
The author also express his thanks to Mr.E.Tsukasaki for
providing computation facilities.
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Publi-cation list
1.Y.KOHZUKI, T.OHGAKU, and N.TAKEUCHI, "Interaction between a dislocation and impurities in KCI single crystals" J.Mater.Sci.
:2:w8 (1993) 3612•
2.Y.KOHZUKI, T.OHGAKU, and N.TAKEUCHI, "Influence of a state of
impurities on the interaction between a dislocation and
impurities in KCI single crystals" J•.Mater.Sci. 28, (1993)
6329.