Atomic structure at the nanoscale a 21st century materials challenge

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CuIr2S4: effect of x-ray irradiation

T. Furubayashi et al., Solid State Comm. 126, 617 (2003).

V. Kiryukhin et al.,

PRL 97, 225503 (2006).

Cubic

Fd-3m

Triclinic

P-1

Tetragonal

I41/amd

Long range

ordered dimers

When x-ray irradiated

no long range ordered

dimers

IC

C

Insulator

Metal

- Incommensurate (IC) short range

state below ~40K

- Commensurate (C) short range

state 40K<T<~100K

HIGHLIGHT

Slide 27

CuIr2S4: local structure view of Metal-Insulator transition

Issues:

Do the dimers survive locally when the long range order is removed by:

temperature

Cr-doping

x-ray irradiation

Total Scattering Approach:

Crystallography – sensitive

to long range ordered dimers

Atomic PDF – sensitive to presence of dimers

Cubic

Fd-3m

Triclinic

P-1

Tetragonal

I41/amd

Long range ordered

dimers

no long range ordered

dimers

IC

C

Insulator

Metal

HIGHLIGHT

Slide 28

Neutron PDF experiment: Ir resonance issue

HIGHLIGHT

Slide 29

CuIr2S4: T-driven Metal-Insulator transition

30s

Dramatic changes observed in the local structure, consistent with crystallography (T=10K)

R. Endoh et al.,

PRB 68, 115106 (2003).

Compare the case where the MI

transition is not crossed! (T=10K)

HIGHLIGHT

Slide 30

Structure of LaMnO3 across the JT-transition at 720 K

30s

Distortions persist locally!

700 K data (blue) vs 750 K data (red)

LaMnO3: utilizing intuitiveness of PDF - simplicity

HIGHLIGHT

Slide 31

CuIr2S4: T-driven Metal-Insulator transition

30s

Dramatic changes observed in the local structure, consistent with crystallography (T=10K)

R. Endoh et al.,

PRB 68, 115106 (2003).

Compare the case where the MI

transition is not crossed! (T=10K)

HIGHLIGHT

Slide 32

CuIr2S4: Hysteretic structural behavior observed

Phase 2: Triclinic P-1 @180 K

Phase 1: Cubic Fd-3m @230 K

Fraction of dimerized sample

from 2-phase fit

R. Endoh et al.,

PRB 68, 115106 (2003).

HIGHLIGHT

Slide 33

CuIr2S4: Cr-doping driven Metal-Insulator transition (5% Cr-doping)

30s

Dimers disappear locally when Insulator-Metal transition is invoked by Cr-doping at 200K