Ferroelectric microregion in KTa1−xNbxO3and SrTiO3

Uwe, Hiromoto; Yamaguchi, Hiroshi; Sakudo, Tunetaro

doi:10.1080/00150198908216758

Cited by 64 publications

(47 citation statements)

References 5 publications

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“…In addition to these components, a sharp peak exists at 45 cm −1 and it is assigned to the A 1g mode according to previous reports. 4,20 The present result on STO16 is in good agreement with the previous results by Sekine et al 21 and Uwe et al 22 Figure 2͑b͒ shows the x͑yy͒-x Raman scattering spectra of STO18-23. In this case, we observed successfully the spectrum in the frequency range from 4 to 80 cm −1 in the backscattering geometry.…”

Section: Resultssupporting

confidence: 82%

“…The origin of the broad component has been considered to be caused by the phonon-branch scattering of the higherharmonic component of the soft E u mode. 22,24,25 In the same way as was done in previous studies, we calculated the spectral shape of the broad component by the phonon-branch scattering model reported by Uwe et al 24 According to this model, the spectral shape of the broad component is given by…”

Section: A Spectrum Analysismentioning

confidence: 99%

“…͑1͒ was calculated with the approximation that the damping of the soft mode is ignored. 22,24,25 That is, the spectral shape of the soft E u mode was assumed to be a ␦ function. However, this approximation does not give any good fit to the frequency part of the broad component lower than 0 .…”

Section: A Spectrum Analysismentioning

confidence: 99%

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Isotope effect on the soft-mode dynamics ofSrTiO3studied by Raman scattering

et al. 2005

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The oxygen isotope effect on the soft-mode dynamics in quantum paraelectric SrTi͑ O atoms are 0.23 ͓STO18-23͔ and 0.32 ͓STO18-32͔, which are less than the critical value x c ͑=0.33͒. In STO18-32, whose exchange rate is just below x c , the soft E u mode shows hardening behavior in a low-temperature region indicating the onset of local ferroelectric order. On the other hand, the soft E u mode in STO18-23 does not show any hardening behavior until 0 K. The enhancement of the inhomogeneity in the crystal by the exchange of 18 O is concluded to play an essential role in the soft-mode dynamics of the quantum paraelectric and ferroelectric STO18-x. The relation between the soft-mode dynamics and quantum fluctuation is discussed.

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Section: Resultssupporting

confidence: 82%

Section: A Spectrum Analysismentioning

confidence: 99%

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Isotope effect on the soft-mode dynamics ofSrTiO3studied by Raman scattering

et al. 2005

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“…17 Uwe et al have shown that introducing oxygen vacancies into a nominally pure SrTiO 3 crystal leads to appearance of local regions of ferroelectric polarization. 18 Infrared reflectance studies of highly reduced SrTiO 3 showed the presence of oxygen vacancies to cause hardening of the TO phonon. 19 It is important to know, which of these factors plays a more significant role in determining the thin films behavior.…”

Section: -9mentioning

confidence: 99%

Raman study of oxygen reduced and re-oxidized strontium titanate

et al. 2007

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We report Raman study of oxygen-reduced single crystal strontium titanate. Oxygen reduction leads to the appearance of the forbidden first order Raman peaks, as well as new spectral features attributed to the local vibrational modes associated with oxygen vacancies. This assignment is supported by ab initio calculations of phonon modes in SrTiO 3 with introduced oxygen vacancies.Raman studies of re-oxidized samples show the same spectra as the initial single crystals. Comparison of Raman spectra of SrTiO 3 thin films and reduced SrTiO 3 single crystals demonstrates the importance of other factors such as polar grain boundaries in the lattice dynamical behavior of thin films.

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“…The defect chemistry studies show, however, that the existence of these impurities, as well as cation off-stoichiometry, often results in oxygen vacancies in the titanates [29]. It was shown by Uwe et al that when a nominally pure STO single crystal is made oxygen deficient, ferroelectric micro-regions are induced in it [30]. Both theory and experiment show that the singly-charged oxygen vacancies give rise t o dipole centers [31, 321.…”

Section: Symmetry Breaking In Sto Films Observed By Raman Scatteringmentioning

confidence: 99%

Vibrational and Electronic Properties of Fullerene and Carbon-Based Clustors. Final Reports for period July 1, 1997 - June 30, 2001

Xi¹

2002

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Reporting period: 7-1-1997 to s-3f@ya$ n,a,.h ,~~~~~~~ doe yov This project was under the direction of Prof. Xiaoxing Xi since Septemter 1997 when the the former PI, Prof. Jeff Lannin passed away. The main focus of the research has been in the lattice dynamics of ferroelectric thin films. In this report, we summarize the results of this project during this period and the publications resulted from this work. Central importance of the soft mode in ferroelectricsThe potential of using ferroelectrics in various device applications have initiated a broad interest in the fundamental properties of ferroelectric thin films. For example, the ferroelectric properties are explored for non-volatile ferroelectric random-access memories (FRAM) [ 1, 21, the high static dielectric constant for dynamic random-access memories (DRAM) [3, 41 and gate oxide in MOSFET [5, 61, and the dielectric nonlinearity for tunable microwave devices [7].Lattice dynamics is of central importance for ferroelectrics [8]. The hallmark of ferroelectricity, i. e. the spontaneous polarization, arises from a displacement of the center of positive charge with respect to the center of negative charge in the ferroelectric crystal. This displacement, such as that of the Ti ion with respect to the oxygen cage in the Ti06 octahedra in BaTiOs (BTO), involves the same ionic movement as the vibration of a zone-center transverse optical phonon mode, the %oft mode". The soft mode has a low frequency due to the interplay between the local restoring force and the long range dipole interaction, and it decreases a s the temperature is lowered. When the temperature approaches a Curie temperature T,, the soft-mode frequency tends to zero 19,10) and the soft mode is frozen in the crystal, which transforms t o a ferroelectric phase [ l l ] . The soft-mode theory, due to Cochran [ll] and Anderson [12], has been proven by many lattice dynamics studies.The soft-mode behavior can explain the high dielectric constant in the paraelectric phase of ferroelectrics. According to the Lyddane-Sachs-Teller (LST) relation, which connects the macroscopic dielectric constants to the microscopic parameter -optical phonon frequencies, for a crystal with N optical modes. Here ~ ( 0 ) and E ( W ) are the static and the high frequency dielectric constants, and W L O~ and W T O~ are the frequencies of the longitudinal and transverse optical phonon modes, respectively. It is generally found that the frequencies of the higher optical modes exhibit no sizeable variation with temperature. The decrease in the soft-mode frequency as the temperature approaches T, will thus cause a dramatic increase of ~( 0 ) .In bulk STO crystals

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Ferroelectric microregion in KTa_1−xNb_xO₃and SrTiO₃

Cited by 64 publications

References 5 publications

Isotope effect on the soft-mode dynamics ofSrTiO3studied by Raman scattering

Isotope effect on the soft-mode dynamics ofSrTiO3studied by Raman scattering

Raman study of oxygen reduced and re-oxidized strontium titanate

Vibrational and Electronic Properties of Fullerene and Carbon-Based Clustors. Final Reports for period July 1, 1997 - June 30, 2001

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