M~oron, Vol.]3, No.3, pp.245-246, 1982. 0047-7206/82/030245-02503.00/0 Printed in Great Britain Pergamon Press Ltd.

HIGH-RESOLUTION IMAGING OF REDUCED RUTILES

D.J. Smith a, M.G. Blanchin b and L.A. Bursill c

High-resolution electron microscope, Cambridge University, Free School Lane, Cambridge,U.K. D~partment de Physique des Mate@iaux, Universit6 Claude Bernard, Lyon i, 43 Boulevard du Ii Novembre 1918, 69622, Villeurbanne, France

CSchool of Physics, University o£ Melbourne, Parkville, 5052, Vic., Australia

Classical point defects, either Ti 3+ interstitials or 02- vacancies, seem unlikely in slightly-reduced rutile, according to Pauling's electrovalance criterion. The observation of (152} crystallographic shear planes (CSP) in an annealed slowly-cooled specimen of TIO1.9986 supported this assertion I . Against this, electrical conductivity measurements 2 indicate three regions of behaviour: I a solid solution Ti02_ x containing isolated point defects; II a two-phase mixture o£ Ti02. x and Tin02_ 1 (n=36,(152)CSP); III a series of one- and two-phase regions TinO2n_l, 4 $ n $ 36. Diffraction contrast studies showed no CSP in samples cooled rapidly from 1525K but CSP appeared in slowly-coole~d or reduced and deformed specimens, suggesting that for TIO1.9965 2.0000 at temperatures > 1500K the equilibrium phase is TiO2_ x. Seven reduced rutiles were therefore studied by HREM in attempts to find new types of defect or CSP fine structure in this region.

Specimens were sectioned from bulk preparations (SxSx2mm 3) and ion-thinned for electron microscopy. Specimen treatments and a summary o£ defects observed appear in Table I. Fig.l shows the cooling curves. Images for specimens 3,7 have been published 4 or submitted 5. Note especially that the most rapidly cooled specimens (1,2,5) showed no CSP, although 2 and 5 showed {I00} precipitate-type contrast whereas 1 showed patchy cha'nges in background, superimposed on [001] lattice images. This may indicate point defect clustering but cannot at present be distinguished from ion-beam damage. Specimens 5,4,6,7 showed new defects~ apparently decorating normal CSP. These lie approximately parallel to {I00}. Grossly internally disordered CSP were observed for specimens 5 and 74,5 whereas relatively well- ordered and aligned CSP occurred in the slow-cooled TiOl.gg65 (specimen 6). Topological considerations imply the decoration defects form after the CSP, presumably at lower temperatures. The {100} defects are tentatively interpreted as precipitates having structure related to M203 (corundum-type, with .3 • • • ~+ 3 + - M=TI and/or impurltles Fe or Cr ) slnce Fe203 precipitates from futile, even at the 1 at % level, in just this way, when natural rutiles are heated at 600°C for a few minutes 6.

Much detailed interpretation remains but it is already possible to make three significant conclusions: I CSP are no__~tpresent, even en miniature, in specimens rapidly cooled from 1300K; II the CSP which are observed on slower-cooling show both lateral and longitudinal disorder which is strongly-dependent on precise cooling history, both the rapid initial drop and tail are significant; III the nature of defects in the "solid solution" TiO2_x, which preferably have a more subtle but crystallochemically reasonable structure than interstitials or vacancies, remains an open question.

The SRC (UK) and CNRS (France) provided experimental facilities. Most o£ the micrographs were obtained with the Cambridge University 600kV HREM. M. Vrinat helped prepare the specimens in Lyon.

500KV image revealing step sequence disorder within CSP (TIO1.9985) 245

246 D.J. Smith, M, G. Blanchin and L. A. Bursi]l

Specimen Reduction

1 Ti01.9994

2 Ti01.9985 A

3 Ti01.9985 B

4 Ti01.9970 B

5 Ti01.9965 A

6 Ti01.9965 C

7 Ti01.996S B

(plus strain 0.038 at 5×10 -5 s -l)

Table i

Cooling Curve (cf Fig. i)

A

Defects Observed

None

{I00} precipitates

Single and paired, disordered and decorated {132} CSP

Decorated {132} CSP

{i00} precipitates

Relatively well-ordered and decorated {132} CSP

Decorated {143} CSP and {011} microtwin lamellae

REFERENCES

1. L.A. B u r s i l l and B.G. Hyde, P h i l . ~.~ag. 23, 3 (1971) . 2. J . P . Baumard, D. P a n i s , A.M. Anthony, J . S . S . Chem. 20, 43 (1977) . 3. M.G. B l a n c h i n , P. P a i s a n t , C. P i c a r d , ~4. Ezzo, G. F o n t a i n e , phys . s t a t . s o l i d i A60,

351 ( 1 9 8 0 ) . 4. M.G. Blanchin, L.A. Bursill, J.L. Hutchison and P.L. Gai, J. de Physique, 42,

Colloque C-3 "Dislocations and Defects in Oxides", Supplement au no. 6, C3-95 (1981). 5. L.A. Bursill, M.G. Blanchin and D.J. Smith, "Disorder within rapidly cooled

Ti01.9985" , submitted 1982. 6. A. Putnis, J. Phys. Chem. Minerals 3, 183 (1978).

1300

v

fl_

I , I I--

1050

80C

55

B

300

TIME (h) Fig.l Cooling curves iii zone image of Ti01.9970 showins

decoration defects on CSP