Raman Scattering from the Soft Phonon in Sr2Nb2O7 for the Phase Transition at 117 K

Ohi, Kikuo; Omura, Hiroshi; Kazumi, Takao; Takashige, Masaaki; Jang, M. S.; Nakamura, Terutaro

doi:10.1143/jpsj.51.3745

Cited by 10 publications

(3 citation statements)

References 11 publications

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“…A remarkable dielectric anomaly along the b-axis has been observed at 117 K [8] where the spontaneous polarization appears in the bc-plane. The lattice instability studies carried out by the Raman scattering experiments revealed the soft optic modes responsible for the first [9] and second [10] ferroelectric phase transitions, and for the normal-IC phase transition [11]. The infrared active soft modes, responsible for paraelectricferroelectric transition were also observed.…”

Section: Introductionmentioning

confidence: 91%

Acoustic and thermal properties of strontium pyroniobate single crystals

Shabbir

Kojima

2003

J. Phys. D: Appl. Phys.

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High resolution Brillouin scattering and modulated differential scanning calorimetry (MDSC) experiments were performed to study the acoustic and thermal properties of strontium pyroniobate (Sr2Nb2O7) single crystals. The anomalous temperature dependence of the longitudinal acoustic phonon mode frequency corresponding to c22 elastic stiffness coefficient was observed in the neighbourhood of the normal-incommensurate phase transition temperature Ti (491 K). The specific heat measured by MDSC showed an anomaly around 487±2 K. The changes in enthalpy and entropy of the phase transition were estimated as 147 J mol−1 and 0.71 J mol−1 K−1, respectively.

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Section: Introductionmentioning

confidence: 91%

Acoustic and thermal properties of strontium pyroniobate single crystals

Shabbir

Kojima

2003

J. Phys. D: Appl. Phys.

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“…Raman [15] and ESR [17] experiments showed a non-classical behaviour of the IC order parameter with critical exponents β = 0.38 and β = 0.34 for the Raman soft mode frequency appearing below T i and the amplitude of the IC wave modulation, respectively. In the a(bc)a and b(ac)a Raman spectra the lowest modes partially soften towards T 0 and then harden [14,18]. Also submillimetre E c spectra [19] revealed another soft mode which hardens below T 0 from 13 to 18.5 cm −1 .…”

Section: Introductionmentioning

confidence: 99%

Polar phonons and far-infrared amplitudon in Sr₂Nb₂O₇

Buixaderas

Kamba

Petzelt

2001

J. Phys.: Condens. Matter

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Polarized far-infrared reflectivity and transmission measurements of an Sr2Nb2O7 single crystal were performed in the temperature interval 10-550 K for the E||a and E||c polarizations. Modes at the centre of the Brillouin zone were analysed in the subsequent paraelectric-ferroelectric-incommensurate-monoclinic phases and the factor group analysis together with the correlation of the modes is presented. The ferroelectric A1 soft mode revealed in Raman spectra below Tc = 1613 K was found in the E||c polarized infrared spectra. An amplitudon which softens to Ti = 488 K was observed in the incommensurate phase. On cooling the amplitudon anti-crosses a hard excitation near 33 cm-1 located in discommensurations and then, at about 100 K, also the ferroelectric soft mode. No evidence was found for the earlier suggested multiplication of the unit cell below the phase transition at T0 = 117 K. Neglecting the small volume of discommensurations, we suggest the Pb11-C2S space group (Z = 4) for the monoclinic phase below T0.

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“…It was known that the octahedra distort and tilt on cooling and SN undergoes three phase transitions at 1342, 215 and −156 • C, Cmcm → Cmc2 1 → Pbn2 1 → Pb11 [6,7]. The dynamics of phase transitions has been studied mainly by means of Raman scattering [8][9][10][11], ESR [12], and polarized far-infrared reflectivity and transmission measurements [13]. The ferroelectric soft mode was found in b(cc)b scattering geometry below T c = 1342 • C. Below 215 • C another soft mode appears showing the displacive character of this normal to incommensurate phase transition.…”

Section: Introductionmentioning

confidence: 99%