SPring-8粉末材料構造解析研究会（第4回）〜 材料構造解析のための最新手法情報 〜（社）日本化学会 化学会館７Fホール

2012年9月11日（水）14:50 – 15:20

セラミックス材料における優れた誘電特性創出のための構造物性研究
黒岩 芳弘
広島大学 大学院理学研究科 物理科学専攻
kuroiwa@sci.hiroshima-u.ac.jp

Structural Study of Ferroelectrics at BL02B2 in SPring-8
1. イントロダクション
1-1. 強誘電体と反強誘電体

2. ペロブスカイト型誘電体のプロトタイプ構造の特徴と相転移
2-1. トレランスファクターと相転移2-2. PZTのMPB形成とプロトタイプ構造の特徴
B
3. チタン酸バリウム−ニオブ酸カリウムナノ複合セラミックスの界面構造と誘電特性
O
3-1. 元素戦略とMPBエンジニアリング
3-1. BaTiO3-KNbO3 ナノ複合材料の結晶構造

4.

まとめ
4-1.誘電物性と結晶構造の一対一対応研究の重要性イントロダクション−強誘電体と反強誘電体−

強誘電体
強誘電性
電圧ゼロでも電荷を蓄える機能をもっている．
電圧を印加する方向を逆転することにより，分極方向を変化させることができる．
圧電性
電圧を印加すると結晶が歪む．一方，外力を加えて結晶歪ませようとすると分極する．

NSSN

Perovskite-type Oxide- antiferrodistortive and ferrodistortive instabilities
inherent in prototype structure

Prototype structure of ABO3 perovskite-type oxide: CubicBOA

A: (0, 0, 0)
B: (0.5, 0.5, 0.5)
O: (0.5, 0.5, 0), (0.5, 0, 0.5), (0, 0.5, 0.5)

Antiferrodistortive instability
BO6 tilt driven perovskiteFerrodistortive instability
B-site off-centering driven perovskite

Slater modeM3 modeR25 mode

If A is Pb or Bi, A-site off-centers

Last modeペロブスカイト型誘電体のプロトタイプ構造の特徴と相転移−トレランスファクターと相転移−− PZTのMPB形成とプロトタイプ構造の特徴−

Mode Classification by Tolerance Factor- relationship between crystal structure and phase transition –simple classification to predict phase transitions

Tolerance factor t :1 rA  rO
0.8  t  1.1
2 rB  rO

ABO3 Perovskite

rA, rB, rO : ionic radiust>1
B atom environment: ample
t=1ideal tolerance e.g. SrTiO3
t<1
B atom environment: scanty
perovskite ionic radius ionic radius toleranceoxide
A ion (Å) B ion (Å)
factorBaTiO3KNbO3
KTaO3
PbTiO3
SrTiO3
NaNbO3
PbZrO3
PbHfO3

1.61
1.64
1.64
1.49
1.44
1.39
1.49
1.49

0.61
0.64
0.64
0.61
0.61
0.64
0.72
0.71

1.07
1.06
1.06
1.03
1.00
0.97
0.97
0.97

AB

O

Ferro-distortive, q = 0（phase transition at zone center)q ≠ 0 (105 K)， q = 0 (<0 K)
Antiferro-distortive, q ≠ 0（phase transition at zone boundary）

MEM Charge Density Maps of NaNbO3 & KNbO3
in Cubic Structure on Nb-O Plane
NaNbO3 (TC = 916 K M3)
NbO

KNbO3

(TC = 707 K 15)

a = 3.94642(1) Åt = 0.97

a = 4.03074(1) Åt = 1.06

1000 K

1000 K

Nb-O plane

Structure parameters of PZTin Cubic Structure at 850 K
PZTStructure parameter of PZT(harmonic model)

Phase diagram of PZT

t=1
PbZrO3

t=1

PbTiO3

B. Jaffe et al., “Piezoelectric Ceramics” Academic Press, London, (1971) 136

t = 0.97

t = 1.03

Y. Kuroiwa et al., Jpn. J. Appl. Phys. 44 (2005) 7151

Disordered Structure of PZT in Cubic Phase111 disorder110 disorder

850 KorderPbZrO3

PbTiO3MPB

110 disorder

Y. Kuroiwa et al.: JJAP 44 (2005) 7151.

チタン酸バリウム− ニオブ酸カリウムナノ
複合セラミックスの界面構造と誘電特性−元素戦略とMPBエンジニアリング−− BaTiO3-KNbO3 ナノ複合材料の結晶構造−

Lead-free Piezoceramics(K, Na)NbO3-LiTaO3(-LiSbO3)

Enhanced Piezoelectric Response of BaTiO3-KNbO3
Composites with Heteroepitaxial Interface
I. Fujii et al.: Appl. Phys. Lett. 99 (2011) 202902.

Artificial Interface
between Polar Nano-BT
Region and KNBTKNKNBTKN on BT
BT: nano-particle 300 nm
BT-KN Composites with Heteroepitaxial Interface (HE I/F)

☺ d33 = 136 pC/N (w HE I/F),☹ d33 = 40 pC/N (w/o HE I/F)

Strain vs. Electric-field Curves

Size Effect of BaTiO3 Nanoparticles withGradient Lattice Strain Layer (GLSL)
T. Hoshina et al. : Appl. Phys. Lett. 93 (2008) 192914.

T. Hoshina : 日本結晶学会誌 51 (2009) 300.

Particle-size Dependence of Dielectric ConstantComposite Structure Model of BaTiO3 Nanoparticles

Experimental
Synthesizing BaTiO3-KNbO3 nano-composite
ceramics with heteroepitaxial interface
Solvothermal method
KOH + K2CO3 + Nb2O5 +BT03 (300 nm), EtOH
20 hrs @230℃

Dielectric constant2 x 2 x 0.5 mm3
1 MHz (HP4294A) @RT

Characterizing crystal structures which govern
dielectric properties
SR powder diffraction
SPring-8 BL02B20.67 Å (18.5 keV) @RT

Rietveld analyses

9 samples：KN/BT = 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0

Rietveld Profile Fitting for BT-0.5KNIobs
Ical

Iobs - Ical
peak position(200)RWP = 3.046%
RI = 2.422%

sinθ/λ [Å-1]Intensity [arb. units]

Intensity [arb. units]

RWP =8.601%
RI = 3.979%

sinθ/λ [Å-1]Upper: BT(tetra) + KN(ortho)
Lower: BT(5 tetra with different c/a and cubic) + KN (ortho + 2 cubic with different a)Core/Multi-Shell Structure Model of BT-0.5KN

BT-0.5KN

Lattice constant [Å]Distance from
center of particle (nm)Tetra. 3 Tetra. 4
Cubic
Tetra. 2
Tetra. 1
Tetra. 0 (core)
Number of components
Validity of Six Components in Analyzing
BT Structure of BT-KN Composites

Distance from center of particle [nm]Variation of Lattice Constants in BT-0.5KN

BT multi-shells with less c/athan BT core
BT
Vmulti-shell = 87.57%

Relationship between Relative Permittivity and
Structural Characteristics

PSPS

r

Molar ratio of KN / BTPS

BT
Vmulti-shell[×106 nm3]

Variations in r and VBT-T1 ~ T4

Variation of c/a of BT and co/bo of KN

Distance from center of particle [nm]Bulk CrystalMolar ratio of KN / BT

BT(tetra.) : a = 3.9933 Å, c = 4.0364 Å, V1/3 = 4.0076 ÅKN(ortho.) : a = 3.967 Å, b’ = c’ = 4.035 Å, a = 90.22º, V1/3 = 4.0151 Å (primitive)

The volume of the distorted interface region of BT and the dielectric property show a similar
trend in the variation of the KN/BT molar ratio, which suggests that the electrically soft interface
between KN and BT governs the dielectric properties of the KN/BT composite ceramics.

PSPSKN thickness [nm]c/a or co/boV1/3 [Å]Structural Characteristics of BT-KN Compositespresent study
STEMPS

molar ratio of KN / BT
Distance from center of particle [nm]Variation of Unit Cell Volume andc/a ratio in BT-0.5KN

Thickness of KN Layer estimated by
Rietveld Refinement and STEM Observation

まとめ−誘電物性と結晶構造の一対一対応研究の重要性−

BT-KNナノ複合セラミックスの界面構造と誘電特性 まとめ

BT-KNナノ複合セラミックスの界面構造を解析し，core/multi-shell構造モデルを提案した．
BTの界面領域がナノ複合セラミックスの誘電特性と密接な関係にある．

BTVmulti-shell[×106 nm3]

r

Lattice constant [Å]

複雑な物質系に対しては，誘電物性と結晶構造を一対一に対応させた議論が必要．

Distance from center of particle [nm]Molar ratio of KN / BTE. Magome et al : Jpn. J. Appl. Phys. 51 (No.9) (2012) in press.