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Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ in high-temperature phases

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 60(SF), p.SFFA08_1 - SFFA08_10, 2021/11

 Times Cited Count:4 Percentile:38.22(Physics, Applied)

Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (abbreviated as BNT) is a lead-free material but exhibits relatively large piezoelectric properties, a lot of researches have been conducted. We performed local structural analysis using high-quality BNT with a stoichiometrically correct composition, and found a chemical order structure of Bi/Na in locally. BNT undergoes a phase transition to a cubic phase at 400$$^{circ}$$C. We estimated that a new disorder structure will appear in the high-temperature phase. In the high temperature phase, pair distribution function (PDF) analysis using synchrotron radiation high-energy X-rays was performed. As a result, we found that Bi shifts from 200$$^{circ}$$C, and this shift becomes an order parameter for the phase transition.

Journal Articles

Nanoscale structural analysis of Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Noguchi, Yuji*

Journal of Physics; Condensed Matter, 33(3), p.035401_1 - 035401_8, 2021/01

 Times Cited Count:4 Percentile:34.98(Physics, Condensed Matter)

Nanoscale structural analysis of relaxor Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$ (PMN) was performed using synchrotron high-energy X-ray diffraction measurements. Although PMN is a well-known relaxor ferroelectric material, the average structure is a cubic structure, and various models have been proposed to explain the ferroelectric microstructure. We performed a wide-range local structure analysis up to 20 nm using the pair distribution function (PDF). As a result, it was found that the structure of PMN changed depending on the distance and it was a glass-like structure.

Journal Articles

Nanoscale structural analysis of Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Noguchi, Yuji*

Japanese Journal of Applied Physics, 59(SP), p.SPPA01_1 - SPPA01_7, 2020/11

 Times Cited Count:18 Percentile:78.55(Physics, Applied)

We investigate A-site cation ordering in the ferroelectric perovskite Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (BNT) by synchrotron X-ray total scattering. Although BNT has a problem of a low depolarization temperature, it is promising a lead-free piezoelectric material. Since the depolarization temperature is presumed to correspond to a relaxer like gradual order-disorder phase transition, local structure analysis is necessary to understand the structure of the diorder phase. Through this approach, the elusive connection between chemical heterogeneity and structural heterogeneity is revealed. Because of the large randomness, the Ti off-center shift is averaged out beyond the unit cell and the structure becomes very close to the average structure beyond the unit cell.

Journal Articles

Local structure analysis of PbTiO$$_3$$ in high-temperature cubic phase

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Kitanaka, Yuki*; Noguchi, Yuji*

Ferroelectrics, 538(1), p.57 - 62, 2019/05

 Times Cited Count:5 Percentile:27.81(Materials Science, Multidisciplinary)

High-energy X-ray diffraction study was performed on lead titanate (PbTiO$$_3$$). Short-range order structure was revealed using atomic pair-distribution function (PDF) method. In the high-temperature cubic phase, there is a large deviation between local and average structure. Especially, Pb atoms deviated from the cubic lattice framework, but establish Pb-O-Pb random network.

Journal Articles

Local structure analysis of BaTiO$$_3$$ modulated by Mn substitution

Yoneda, Yasuhiro; Kohara, Shinji*; Noguchi, Yuji*; Miyayama, Masaru*

Transactions of the Materials Research Society of Japan, 40(1), p.29 - 32, 2015/03

Barium titanate (BaTiO$$_3$$) with a high dielectric constant is widely used in the production of ceramic capacitors. However, during sintering large numbers of ionized oxygen vacancies and conduction electrons are created. Doping with manganese is one of several ways to confine the electrons to a small region. In Mn-doped BaTiO$$_3$$ there exist three valence states for the manganese ions, Mn$$^{2+}$$, Mn$$^{3+}$$, and Mn$$^{4+}$$. The Mn$$^{4+}$$ is nearly exactly incorporated into Ti$$^{4+}$$ sites and participates in the collective motion in the lattice. We performed local structure analysis by using atomic pair-distribution function (PDF) and X-ray absorption fine structure (XAFS). Figure 1 shows the obtained PDFs for pure BaTiO$$_3$$ and 0.5%-Mn-doped BaTiO$$_3$$. All data collected at room temperature. Two obtained PDF patterns are well in agreement. Mn doping has hardly affected local structure.

Journal Articles

Damped soft phonons and diffuse scattering in (Bi$$_{1/2}$$Na$$_{1/2}$$)TiO$$_{3}$$

Matsuura, Masato*; Iida, Hiroyuki*; Hirota, Kazuma*; Owada, Kenji; Noguchi, Yuji*; Miyayama, Masaru*

Physical Review B, 87(6), p.064109_1 - 064109_10, 2013/02

 Times Cited Count:28 Percentile:74.56(Materials Science, Multidisciplinary)

Neutron-scattering studies of (Bi$$_{1/2}$$Na$$_{1/2}$$)TiO$$_{3}$$ (BNT) have been performed to elucidate the microscopic mechanism of the broad maximum in the temperature dependence of the dielectric constant at Tm $$sim$$ 600 K and the reduction in the piezoelectric properties above the depolarization temperature, 460 $$sim$$ 480 K. We observed diffuse scattering near the $$Gamma$$ point below 700 K, which competes with the superlattice peak at the M point of the tetragonal phase but coexists with the superlattice peak at the R point of the rhombohedral phase. The diffuse scattering shows an anisotropic Q shape extending along the $$<$$100$$>$$ direction transverse to the scattering vector Q, which is explained by atomic shifts bridging the tetragonal and rhombohedral structures. We propose that the broad maximum in the dielectric constant is associated with a diffusive first-order transition between the competing tetragonal and rhombohedral phases. In addition, we found that the diffuse scattering is reduced for single crystals grown under high oxygen pressure, which suggests an analogy with the central peak in hydrogen-reduced SrTiO$$_{3}$$. Inelastic neutron scattering near the $$Gamma$$ point reveals a heavily overdamped soft mode similar to those reported in lead-based relaxors, the "waterfall" feature. Moreover, a damped soft transverse acoustic mode is observed for the $$<$$100$$>$$ direction as the anisotropic diffuse scattering, indicating phase instabilities with the same origin as that of the diffuse scattering. The recovery of the soft mode is observed near the depolarization temperature, which coincides with the disappearance of the superlattice peak at the M point. These results indicate that the depolarization and the waterfall feature originate in the dynamic nature of ferroelectric clusters in the coexisting tetragonal/rhombohedral phase.

Journal Articles

Electronic and local structures of Mn-doped BiFeO$$_3$$ crystals

Yoneda, Yasuhiro; Kitanaka, Yuki*; Noguchi, Yuji*; Miyayama, Masaru*

Physical Review B, 86(18), p.184112_1 - 184112_11, 2012/11

 Times Cited Count:60 Percentile:89.25(Materials Science, Multidisciplinary)

The electronic structure of complex oxides is important for understanding their functional properties. Here we report the results of investigating multiferroic BiFeO$$_3$$ using various X-ray spectroscopy techniques. Zn- and Mn-codoped and Mn-doped BiFeO$$_3$$ samples were prepared with the aim of improving ferroelectric properties of BiFeO$$_3$$. The valences of the doped Mn and host Fe were investigated. When oxygen vacancies exist in the sample, Mn acts as a hole acceptor. Furthermore, Mn and Fe stabilize the perovskite unit by changing their ionic radius. As a result, Mn and Fe atoms exhibit various valence states in the BiFeO$$_3$$ system. Evidence of the electronic structure for Fe $$3d$$-O $$2p$$-Bi $$6s$$ hybridization is also presented.

Journal Articles

Effects of oxygen annealing on dielectric properties of LuFeCuO$$_{4}$$

Matsuo, Yoji*; Suzuki, Muneyasu*; Noguchi, Yuji*; Yoshimura, Takeshi*; Fujimura, Norifumi*; Yoshii, Kenji; Ikeda, Naoshi*; Mori, Shigeo*

Japanese Journal of Applied Physics, 47(11), p.8464 - 8467, 2008/11

 Times Cited Count:11 Percentile:42.22(Physics, Applied)

We have investigated the physical properties of LuFeCuO$$_{4}$$, which is a derivative material of the electronic ferroelectric LuFe$$_{2}$$O$$_{4}$$. From electron diffraction measurements at room temperature, ionic ordering of Fe$$^{3+}$$ and Cu$$^{2+}$$ in the a-b plane was observed. This ordering is similar to that in LuFe$$_{2}$$O$$_{4}$$ and has an electric dipole. The observation of small domains (5-10 nm) indicates the presence of polar regions. Dielectric measurements showed that a peak of dielectric constant appeared at around 500 K, and the peak value was about 1000, indicating that LuFeCuO$$_{4}$$ is a dielectric material. We will present the experimental data on the samples prepared under high-pressure oxygen.

Journal Articles

Microstructures related to the ferroelectric properties in BiFeO$$_{3}$$-BaTiO$$_{3}$$

Kitagawa, Shuji*; Horibe, Yoichi*; Yoshii, Kenji; Suzuki, Muneyasu*; Noguchi, Yuji*; Nishihara, Sadafumi*; Hosokoshi, Yuko*; Mori, Shigeo*

Transactions of the Materials Research Society of Japan, 33(1), p.27 - 30, 2008/03

Microstructures related to the ferroelectric (FE) properties in(1-x)BiFeO$$_{3}$$-xBaTiO$$_{3}$$ were examined mainly by a transmission electron microscopy, in combination with conventional magnetic and dielectric measurements. It was found that macroscopic-sized FE domain structures in BiFeO$$_{3}$$changed into fine FE microstructures with the 20-30nm size in the x=0.25compound, as the BaTiO$$_{3}$$ concentration (x) was increased. In addition, we found characteristic tweed-like contrast due to the strain field in the x=0.33 compound at room temperature. We carefully investigated the spatial distribution of the FE microdomains in the x=0.25 compound by obtaining real-space images and determined spatial configuration of the spontaneous polarization in each FE microdomains.

Oral presentation

Relationship between local structure and magnetic/dielectric properties in (1-${it x}$)BiFeO$$_{3}$$-${it x}$BaTiO$$_{3}$$

Ozaki, Tomoatsu*; Nishihara, Sadafumi*; Hosokoshi, Yuko*; Tokunaga, Masashi*; Noguchi, Yuji*; Miyayama, Masaru*; Yoshii, Kenji; Mori, Shigeo*

no journal, , 

We have investigated the local structure and physical properties of (1-${it x}$)BiFeO$$_{3}$$-${it x}$BaTiO$$_{3}$$. Electron-diffraction measurements showed the coexistence of magnetic and ferroelectric nano domains at around x=0.35. Dielectric measurements under magnetic field showed the lack of magneto-dielectric effect, indicating a weak correlation between the magnetic and ferroelectric properties. Magnetization-magnetic field curves showed the existence of magnetic nano domains.

Oral presentation

XAFS study on Mn-doped BiFeO$$_3$$

Yoneda, Yasuhiro; Noguchi, Yuji*; Miyayama, Masaru*; Kitanaka, Yuki*

no journal, , 

BiFeO$$_3$$ is not so large as intrinsic polarization is expected from a crystal structure since the coercive field is very large. However, good hysteresis is obtained by Mn-doping. In order to investigate the Mn dope effect of BiFeO$$_3$$, XAFS measurement was performed by each absorption edge of Bi, Fe, and Mn, and the estimate and local order structure of the valence were conducted. Since the valence and local structure of Mn are changing with annealing, they have suggested the importance of an oxygen deficiency.

Oral presentation

Local structure analysis of PbTiO$$_3$$ in high-temperature cubic phase

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Kitanaka, Yuki*; Noguchi, Yuji*

no journal, , 

Lead titanate, PbTiO$$_3$$, has a tetragonal structure having a large c/a ratio at room temperature. A phase transition to the paraelectric phase at 490$$^{circ}$$C, structural changes to cubic. However, just above the transition point to the paraelectric phase, the phonon modes of the still ferroelectric is observed. Therefore, spontaneous polarization using a sample of reversible high quality, perform high-energy X-ray diffraction experiments were subjected to structural analysis in a wide temperature range from room temperature to 800$$^{circ}$$C. Short range order structure analysis and atomic two pairs distribution function (atomic pair-distribution function, PDF) was performed using. A comparison local structures at room temperature of the observed local structure and relaxor Pb (Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$ (PMN) with 800$$^{circ}$$C of PbTiO$$_3$$, network structure similar to the relaxor PMN is present in the high temperature phase of PbTiO$$_3$$ It is considered to have.

Oral presentation

Local structure analysis of relaxor ferroelectrics Pb(Mg$$_{1/3}$$Nb$$_{2/3}$$)O$$_3$$

Yoneda, Yasuhiro; Taniguchi, Hiroki*; Noguchi, Yuji*

no journal, , 

Many structural models have been proposed for relaxer ferroelectrics Pb(Mg$$_{1/3}$$Nb$$_{2/3})$$O$$_3$$. We have shown that the Pb-O distance obtained from the mean structure differs from the Pb-O distance obtained from the X-ray absorption fine structure (XAFS). Since the deviation between the average structure and the local structure is considered to be derived from the characteristic environment of the Pb atom, the behavior similar to that of the Pb atom in the pyrochlore type Pb$$_2$$ Sn$$_2$$O$$_6$$ is assumed and the local structure is assumed. I tried structural modeling. A pair-distribution function (PDF) analysis was performed, and as a result of local structure modeling, it was suggested that there is a network structure of Pb atoms that is different from the periodicity of the lattice system.

Oral presentation

Local structure analysis of high-quality Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$

Yoneda, Yasuhiro; Noguchi, Yuji*

no journal, , 

Since bismuth sodium titanate (Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$, BNT) exhibits relatively large piezoelectric properties, many studies have been conducted as lead-free piezoelectric materials. Since it is a highly volatile substance containing bismuth and sodium, it was difficult to obtain a chemically correct BNT due to these defects generated during firing. Recent improvements in the synthetic method have made it possible to obtain BNT with a chemical composition, so structural analysis was performed again using high-quality BNT. As a result of local structural analysis, it was found that bismuth atoms shift from the average structural position in the high-temperature region, causing a structural phase transition. (to be published) The diffuse scattering component has a weaker intensity than the Bragg reflection, but we have devised a method to evaluate whether analysis level data is obtained, and we plan to report this as well.

Oral presentation

Preparation and characterization of bismuth-based ferri-dielectric ceramics

Noguchi, Suzunosuke*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*

no journal, , 

The solid solution Bi$$_{(1-x)/2}$$Na$$_{(1-x)/2}$$Ba$$_x$$TiO$$_3$$ (BNT-BT) of the lead-free perovskite ferroelectrics Bi$$_{0.5}$$Na$$_{0.5}$$TiO$$_3$$ (BNT, space group: R3c) and BaTiO$$_3$$ (BT, space group: P4mm) is morphotropic phase boundary (MPB) and has attracted much attention because of its excellent piezoelectricity at MPB. In this study, we aim to control the electric field-induced phase transition and to complete the two-dimensional phase diagram of BNT-BT ceramics before and after the application of an electric field. The dielectric P4bm phase was found to be stabilized at a composition near MPB and with large A-site vacancies in BNT-BT solid solution ceramics.

Oral presentation

Creation of novel ferri-dielectrics and control of their electric-field-induced phase transitions

Fukushima, Kento*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*

no journal, , 

A lead-free perovskite ferroelectric, (Bi,Na)TiO$$_3$$ (rhombohedral R3c), has attracted much attention because it forms a morphotropic phase boundary (MPB) with a tetragonal P4mm ferroelectric [BaTiO$$_3$$, (Bi,K)TiO$$_3$$] and shows excellent piezoelectricity in the MPB. P4bm phase, which exhibits ferri-dielectricity in the vicinity of the MPB, has been found to exist. In this study, we aim to clarify the compositional phase diagram of (Bi,Na)TiO$$_3$$-based solid solution ceramics with strict composition control and to elucidate the whole picture of their polarization properties. bm and the phase boundary between P4bm and P4mm were identified.

Oral presentation

Ferri-electricity in (Bi$$_{1/2}$$K$$_{1/2}$$)TiO$$_3$$-(Bi$$_{1/2}$$Li$$_{1/2}$$)TiO$$_3$$ solid solution

Saito, Kotaro*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*

no journal, , 

In addition to excellent piezoelectricity and dielectric properties, ferri-dielectric phases exhibit giant electric-field-induced strain due to the electric-field-induced phase transition. The presence of ferri-dielectric phase and its properties were investigated for (Bi$$_{1/2}$$K$$_{1/2}$$)TiO$$_3$$-(Bi$$_{1/2}$$Li$$_{1/2}$$)TiO$$_3$$ (BKT-BLT) solid solution ceramics by searching for compositional phase boundaries and evaluating the composition dependence of polarization properties through crystal structure analysis. This study revealed that a ferri-dielectric phase exists around $$x$$ = 8% in the BKT-BLT solid solution system, and that a specifically high relative permittivity can be obtained at this composition.

Oral presentation

Effect of chemical pressure on phase stability of antiferroelectric NaNbO$$_3$$

Aso, Seiyu*; Yoneda, Yasuhiro; Matsuo, Hiroki*; Noguchi, Yuji*

no journal, , 

We have attempted to introduce positive chemical pressure into NaNbO$$_3$$ by replacing Na$$^+$$ with a small Ca$$^{2+}$$. The superlattice reflections originating from the antiferroelectric P phase appeared both before and after the application of an electric field, which confirmed that a reversible electric-field-induced phase transition was achieved.

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