実験報告書様式（一般利用課題・成果公開利用）（ ※本報告書は英語で記述してください。ただし、産業利用課題として採択されている方は日本語で記述していただいても結構です。 ）MLF Experimental Report

提出日 Date of Report
2014.07.30

課題番号 Project No.

装置責任者 Name of responsible person

2014A0182

S. Torii

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）INVESTIGATION OF A UNCONVENTIONAL HYDROGEN

BL-08

GEOMETRIC EFFECT IN

実施日 Date of Experiment

HYDROXYL SALTS CO2(OD)3CL AND CO2(OD)3BR

5/7 9:00 - 5/13 9:00

実験責任者名 Name of principal investigator
X.G. Zheng
所属 Affiliation
Saga University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
Co2(OD)3Cl in powder form

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

Hydroxyl salts of the type M2(OH)3X have been known for a long time. The M2(OH)3X compoundswith the magnetic ions Cu2+, Ni2+, Co2+, Fe2+, and Mn2+ are all magnetic materials. The mostfamiliar might be the hydroxyl chloride Cu2(OH)3Cl (atacamite), which forms naturally on copperand bronze as a green patina and is widely recognized as imparting the characteristic hue to theStatue of Liberty. It may also exist as a bio-minerals in living organisms such as in the jaws of themarine bloodworm and crocodile, where it enhances hardness and stiffness.

However, only inrecent years their magnetic properties became clear and they are known as “frustrated magnets”
due to our research efforts. Our latest finding is a universal strong magnetic--dielectric--latticecoupling in all such compounds.

Measurements of their dielectric constants and lattice parameters

revealed simultaneous changes at their respective TN (TC) for all hydroxyl salts of the type

M2(OH)3X, and M(OH)X, which demonstrates strong magnetic--dielectric--lattice coupling.
Then we further found that for Co2(OH)3Cl, the deuterated compound (Co2(OD)3Cl) clearly showed
ferroelectricity at exceptionally high temperatures.

12. 実験方法及び結果（つづき） Experimental method and results (continued)
To understand its mechanism, we performed a comparative synchrotron X-ray diffraction
experiment for Co2(OH)3Cl and Co2(OD)3Cl. Remarkable and anisotropic change in the unit cell
lengths occurred upon deuteration, with notable difference along the a (a=b) axes than the c-axis
direction. More obvious changes appeared in the atomic bonding lengths with deuteration. We cansee that the distances between the ions neighbored with nearby hydrogen, for example, the bondlength between the Co ions on the kagome plane (Co1-Co1) and those between the O and Co(O-Co1 and –Co2), all notably increased upon deuteration. This is surprising because H and D
have almost equivalent ion radii.
Therefore, we expect that the ferroelectricity in Co2(OD)3Cl can be attributed to the smallchanges in the lattice geometry. Since the hydrogen positions in Co2(OD)3Cl is critical inuncovering its mechanism, they need to be precisely determined. Therefore, we performed neutron
diffraction experiment on Co2(OD)3Cl. A surprising finding is that all atomic positions showedprominent dependency on the temperature (Fig. 1). In special, the atomic positions of D showed anabrupt change at the ferroelectric transition near T = 230 K.

JPARC2014ANeutronCo2OD3ClunifiedParameters

Unified cell parameters&positions

1.004
a0c0
z0_Cl
x0_O
y0_O
z0_O
x0_D
y0_D
z0_D
a+0
c+0
z0_Cl+
x0_O+
y0_O+
z0_O+
x0_D+
y0_D+
z0_D+

1.002

10.998

0.996

04080

Fig.

1

Prominent

temperaturedependency of the atomic positions inCo2(OD)3Cl. All parameters are unifiedwith the respective values at 100 K.

120160

200

240

280

320

T (K)

This makes an important progress in understanding the mechanism for the reported exotic ferroelectricity in
Co2(OD)3Cl.

2