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
2011.6.22

課題番号 Project No. 2010B0016

装置責任者 Name of responsible person

実験課題名 Title of experiment

Takashi Kamiyama

Structural analysis of Pb-free perovskite ferroelectricoxides

装置名 Name of Instrument/（BL No.）
SuperHRPD

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Yuji Noguchi

2011/ 3/ 9 13/ 00 ~所属 Affiliation

2011/ 3/ 11 13/ 00

RCAST, The Univ. of Tokyo
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.
Bi-based perovskite ferroelectric oxides
x(Bi,K)TiO3-(1-x)BiFeO3，x=0.00-0.70

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.
Development of lead-free ferroelectric materials that can replace widely-used lead zirconate titanate(PZT) is becoming increasingly imperative. Ferroelectric BiFeO3 (BFO) with rhombohedral R3c structure
has attracted a great deal of attention because of a very high Curie temperature (TC) of 830 °C and a large
spontaneous polarization (Ps) exceeding 100 μC/cm2 [1]. BFO-based solid solution ferroelectric materials
are expected as materials which can replace PZT. Recently, our group has reported thatx(Bi0.5K0.5)TiO3(BKT)-(1-x)BFO ceramics with x = 0.40 exhibit a large remanent polarization (Pr) of 52
μC/cm2 and a superior piezoelectric property (Smax/Emax = 190 pm/V) [2].
The objective of this study is to investigate the effects of defect control on the fundamental properties ofxBKT-(1-x)BFO single crystals It is demonstrated that defect control (suppression of the formation ofvacancies of Bi and O) at a high oxygen pressure Po2 is effective for obtaining high-quality andhigh-performance xBKT-(1-x)BFO single crystals.
The objective of this study is to elucidate the fundamental structural properties of BKT-BFO through thestructural analysis based on high-resolution neutron powder diffraction study.

12. 実験方法及び結果（つづき） Experimental method and results (continued)【 Sample preparation 】 BKT-BFO powders were prepared by asolid-state reaction. Mixed raw materials were sintered at 800–1000 °C in

x = 0.46

air. High-resolution neutron powder diffraction (NPD) data were collected
x = 0.43

Intensity (a.u.)

by SuperHRPD in KEK, and the data obtained were analyzed by the

1.03
1.02

113hαr59.6
αr (deg.)c/a (-)(c)(b) R3c(a) P4mm006h

111c

Rietveld method using the program Z-Rietveld.
x = 0.40【Results and discussion】Figure 1 shows the NPD patterns around 111c (cdenotes cubic). From the X-ray diffraction (XRD) analysis, 006h and 113h(hx = 0.36
denotes hexagonal) peaks originating from rhombohedral R3c structure wereobserved for x ≤ 0.36. From the NPD analysis for x = 0.40, 0.43, and 0.46,
these peaks attributed to R3c structure were also detected. These results
x = 0.30
demonstrate that R3c phase is present in 0.40 ≤ x ≤0.46. The Rietveld analysis
assuming that two phases composed R3c and P4mm structures are present
0.22
0.230.24
reproduces the NPD data fairly well. Win an increase in x, moral ratio of R3cd (nm)phase decreased, e.g., 83 % for x = 0.30 and 66 % for x = 0.46. Figure 2
Fig. 1 Neutron powder diffraction data
exhibits the structural parameters obtained by the Rietveld analysis, i.e.,around 111c for BKT–BFO (x = 0.30–
tetragonal (P4mm) distortion expressed by c/a (parameter c divided by0.46).
parameter a), rhombohedral (R3c) distortion of αr (60 ° shows zerodistortion). Here, the parameters of BFO (x = 0) and BKT (x = 0) are referred from the Ref. 3 and 4. The samples (x =0.40) that exhibits superior ferroelectric and piezoelectric properties had the values of c/a ~ 1.00、αr ~ 59.6 °. This
results show that x = 0.40 is composed of the R3c phase with an apparent ferroelectric distortion and the P4mm phasewith a very small ferroelectric distortion (hereafter, this phase is referred to as pseudo-cubic phase).

1.0159.4
1.00
0.25 0.30 0.35 0.40 0.45 0.50
x in xBKT-(1-x)BFO

1.00

0.00

0.30

0.35 0.40 0.45
x in xBKT-(1-x)BFO

0.50Fig. 2 Structural parameters of (a) tetragonal distortion of c/a of P4mm phase and (b) rhombohedral distortion arof R3c phase as a function of composition (x) and (c) crystal structure of R3c phase.

[1] J. B. Neaton, C. Ederer, U. V. Waghmare, N. A. Spaldin, K. M. Rabe, Phys. Rev. B, 2005, 71, 014113[2] H. Matsuo, Y Noguchi, M, Miyayama, M, Suzuki, A, Watanabe, S. Sasabe, T. Ozaki, S. Mori, S. Torii, T.
Kamiyama, J. Appl. Phys., 2010, 108, 104103

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