Atomic structure at the nanoscale a 21st century materials challenge

Page
1

Slide 1

Atomic structure at the nanoscale: a 21st century materials challenge

Emil S. Bozin

Applied Physics and Applied Mathematics Department, Columbia University

Condensed Matter Physics and Material Science Department, BNL

Workshop on Characterization of Advanced Materials under Extreme Environments for Next Generation Energy Systems

September 25-26, 2009

Slide 2

Complex nanostructured materials

Images: Igor Levin/Tom Pinnavaia/Sandra Rosenthal

Nanoporous (mesoporous) materials

Nanoparticles

Nanostructured bulk crystals

INTRO

- Complex bulk systems with interesting physical properties are often inhomogeneous on a nanometer lengthscale

high-temperature superconductors, colossal magnetoresistive materials,

high performance thermoelectric materials …

- Nano-particles, nano-tubes, nano-wires etc. important for applications optoelectronics, nanosensors, programmed release drug delivery systems…

Physical properties often critically depend on the nano-scale structure, rather than the long-range structure!

Slide 3

Crystallography gives average structure

ROUTINE

Figures: J.S.O. Evans et al.

and M. Tucker et al.

Bragg peak info ONLY

Rietveld method

in powders

Slide 4

Crystallography challenged: materials w/ disorder

Example: Ho2(Ti2‑xHox)O7-x/2 ”stuffed spin ice”

300K neutron diffraction patterns (GPPD, IPNS, Argonne)

CHALLENGE

Rietveld approach assumption: crystals are perfectly periodic…

…but this is not always the case!

Slide 5

Crystallography challenged: nano-crystals

CHALLENGE

Figures: J.S.O. Evans et al.

and M. Tucker et al.

Bragg peak info ONLY

Rietveld method

in powders

Slide 6

Global Approach

FUTURE

Add complementary information

Extra experimental data

Theoretical constraints

Science, 316, 561 (2007).

Slide 7

What is PDF?

Pair distribution function (PDF) gives the probability of finding an atom at a distance “r” from a given atom.

APPROACH

Slide 8

Pair Distribution Function Method: Applicability

Originally: short range order in liquids and glasses

Since late 1980’s: disorder in crystalline materials