Brillouin spectroscopy of acoustic phonon dispersion in Ba2NaNb5O15 at its incommensurate transition

Young, P. W.; Scott, J. F.

doi:10.1080/00150198308208236

Cited by 15 publications

(3 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Our experiments give T C about 30 K lower than in samples thought to be of lowest Na vacancy concentration [43]. Since the vacancy concentrations in these materials are usually [41] of order 1%-5%, this is in general agreement with the model; i.e., it is of the expected sign and order of magnitude.…”

Section: Disordered Exclusion Modelsupporting

confidence: 81%

“…There has been particular interest in the interaction of mobile point defects with incommensurate antiphase boundaries [38][39][40][41][42]; Toledano et al have shown [38] that these are sodium vacancies (as verified by Oliver and Scott [36]), and Schneck has shown [41] that the vacancy concentration can exceed 10%, depressing T C . These antiphase kinks can propagate very rapidly and give rise to a diffusivity of 1.3 cm 2 s −1 [42,43], approximately 65 times faster than the thermal diffusion at the same temperature, and compatible with theory [44]. Additional studies show [45,46] that this diffusion is hydrodynamic, with a dynamic central mode linewidth whose width is proportional to q 2 , the square of the momentum transfer in laser spectroscopy experiments.…”

Section: Introductionsupporting

confidence: 72%

See 1 more Smart Citation

High temperature phase transitions in barium sodium niobate: the wall roughening 1q–2qincommensurate transition and mean field tricritical behaviour in a disordered exclusion model

Scott

Hayward

Miyake

2005

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

Barium sodium niobate (Ba2NaNb5O15) is a tungsten bronze structure that exhibits a complicated sequence of six structural phase transitions, including three incommensurate (IC) phases. The phases are unusual in that all but the highest temperature P4/mbm structure are ferroelectric. Unlike the situation for most incommensurate insulators, in which ferroelectricity develops at low temperatures along the modulation direction, the polarization direction in barium sodium niobate is orthogonal to the modulation(s), permitting some unusual phenomena. In the present study we analyse the thermal and dielectric behaviour at the Curie temperature TC near 830 K as well as that at the Ccm 21–IC(1q) transition near 543 K, the IC(1q)–IC(2q) transition near 565 K and the IC(2q)–P4bm transition at 582 K. The entropy change at 565 K is related to the wall roughening model of Rice et al (1981 Phys. Rev. B 24 2751). Data near TC = 830 K indicate close proximity to a tricritical point, and discussions of critical exponents are presented, all of which are found to be mean field. Because of Na vacancies, transition temperature variation is found among specimens Ba2Na1−xNb5O15 (830 K< TC(x)< 865 K), and the system appears to be describable by the disordered exclusion model as a slightly first-order intrinsic system whose dynamics are suppressed by weak disorder. Near TC the specific heat C(T) is compared with the random bond prediction of Harris (1974 J. Phys. C: Solid State Phys. 7 1671): C(T) = C0(T)/[1+bx2C0(T)], where C0(T) is the intrinsic specific heat of the vacancy-free crystal varying as (TC−T)−1/2 and x is the sodium vacancy concentration. In agreement with Harris’s model, the shifts in TC(x) are to lower T with increasing x and scale as x; the broadening scales as x2; and the effective critical exponent remains unchanged at α = 1/2.

show abstract

Section: Disordered Exclusion Modelsupporting

confidence: 81%

Section: Introductionsupporting

confidence: 72%

High temperature phase transitions in barium sodium niobate: the wall roughening 1q–2qincommensurate transition and mean field tricritical behaviour in a disordered exclusion model

Scott

Hayward

Miyake

2005

J. Phys.: Condens. Matter

View full text Add to dashboard Cite

show abstract

“…In Ref 14. it is shown that T ( T ) so obtained can be expressed as a mean-field critical slowing-down term plus a T-independent constant: r-'( T ) = t~; l +T;'…”

mentioning

confidence: 99%

New results in incommensurate crystals: Kink diffusion and long‐period lock‐in phases

Scott

1986

J Raman Spectroscopy

Self Cite

View full text Add to dashboard Cite

Two new results for incommensurate phases of crystals are discussed: the experimental observation of a q2 dependence of the inverse relaxation time observed in the hypersonic regime via near-forward Brillouin scattering experiments, tentatively interpreted as kink diffusion, and the theoretical demonstration that long-period lock-in phases observed in crystals which are simultaneously ferroelectric in their incommensurate phases are stabilized by the spontaneous polarization field. This theory explains the observed limits of incommensurate wave vector in BaMnF, as a function of temperature: 2a*/5 = 0.399a* -0.389a* = 5a*/13, where the 2/5 value is the low-temperature limit and the 5/13 value is the high-temperature limit. It also explains one mechanism for stabilizing the 2/5 phase at lower temperatures than are permitted in the ANNNI (axial next-nearest neighbour Ising) model of Yamada and Hamaya in the absence of a spontaneous polarization field. ~~~

show abstract

Dynamic Central Modes and Photorefractive Effects at TI and TC in Barium Sodium Niobate

Oliver

Scott

Lee

et al. 1988

Laser Optics of Condensed Matter

View full text Add to dashboard Cite

Brillouin spectroscopy of acoustic phonon dispersion in Ba2NaNb5O15 at its incommensurate transition

Cited by 15 publications

References 9 publications

High temperature phase transitions in barium sodium niobate: the wall roughening 1q–2qincommensurate transition and mean field tricritical behaviour in a disordered exclusion model

High temperature phase transitions in barium sodium niobate: the wall roughening 1q–2qincommensurate transition and mean field tricritical behaviour in a disordered exclusion model

New results in incommensurate crystals: Kink diffusion and long‐period lock‐in phases

Dynamic Central Modes and Photorefractive Effects at TI and TC in Barium Sodium Niobate

Contact Info

Product

Resources

About