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# Takeshi Egami <egami@utk.edu>
# requesting 6 days days, at minimum=5 days days
# beamline 33ID, Structure of Nickelate with Orbital Frustration
# instrument 33ID-D kappa
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# top:/home/www/beamtime-requests/req00677.txt
# UNICAT Member Beam Time Request  #677
# created Fri Aug 27 12:35:39 CDT 2004
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beamline:
	33ID

collaboration:
	No

collaborator_Paul:
	ON

collaborator_Pete:
	ON

contact:
	egami@utk.edu

days:
	6 days

description:
	Summary:

	High-energy powder diffraction and medium energy single crystal diffraction will be carried out on LiNiO2.  The measurement will complement the neutron scattering results to clarify the detailed structure of this compound with orbital frustration.


Motivation:

	LiNiO2 has a layered structure with a layer of 2-dimensional triangular lattice of Ni3+, which has S=1/2 spin. Since the S=1/2 spin on a triangular lattice can be frustrated and the system shows no sign of magnetic transition this system was considered to be the prototype for the quantum spin-liquid.  However, Ni3+ is also a Jahn-Teller ion because of the singly occupied eg level, while there is no sign of macroscopic Jahn-Teller distortion.  Since the eg level can be described by a pseudo-spin ½, it is possible that the orbital moment is also frustrated.
We carried out a pulsed neutron powder diffraction on LiNiO2 and obtained the atomic pair-density function (PDF) using the NPDF diffractometer at the LANSCE of Los Alamos National Lab., and confirmed local Jahn-Teller distortion.  We found that the local Jahn-Teller distortion is likely to form a trimer lattice with three sublattices, thus resulting in no macroscopic distortion of the lattice.  However, we also found that the trimer order extends only around 8 nm, forming nano-scale domains with different trimer order.  Bragg peaks are broad, suggesting mesoscopic disorder, but the broadening is not uniform, and depends on the index.  We suspect the reason why the trimer order does not become a long-range order is that the layer with the trimer lattice should be spatially curved because the trimer breaks the mirror symmetry, while the crystal structure allows only a flat plane.  We believe that this frustration is the origin of the domain formation. 

Proposed Experiment:

Experiment:
	
	Dave Mandrus and Brian Sales have succeeded in growing a single crystal of this compound.  We will study the diffraction at 12 keV to determine

1.	Superlattice diffraction due to the local trimer order.
2.	Shape of the Bragg peaks.

We have already determined that the Bragg peaks are broad, depending on the index, suggestive of the complex mesoscopic disorder.  We will determine the peak widths and relate them to the structure and domain size.  This measurement will require 6 days, including orienting the sample.

equipment_required:
	Displex

experiment:
	Structure of Nickelate with Orbital Frustration

foreign_nationals:
	Ferenc Stercel
Wojtek Dmowski
Maxim Lobanov (He is not yet in the system; we will put him on)

hazards:
	No hazzard expected.

instrument:
	33ID-D kappa

instrument_other:
	

minimumdays:
	5 days

name:
	Takeshi Egami

nonmembers:
	

unacceptable_dates:
	

z34ID_details:
	


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