Optical Studies of Structural Phase Transitions

Fleury, P. A.; Lyons, K. B.

doi:10.1007/978-3-642-81531-7_2

Cited by 18 publications

(12 citation statements)

References 126 publications

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“…The deviations, which increase in magnitude from ∼700 K towards T c , correlate with the appearance of a quasi-elastic scattering central peak in the Brillouin spectra. Development of a Brillouin central peak of this type is commonly found to be associated with structural phase transitions, including the transition in SrTiO 3 (Lyons and Fleury 1977), and it can be due to a diversity of relaxation mechanisms (e.g., Fleury and Lyons 1979, 1981. As far as the present authors are aware, however, a central peak associated with a transition which involves phases that are neither ferroelectric nor piezoelectric has not previously been observed to occur over such a wide temperature interval.…”

Section: Introductionmentioning

confidence: 52%

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO₃: II. Mechanisms of static and dynamical softening

Carpenter¹,

Sinogeikin²,

Bass³

2009

J. Phys.: Condens. Matter

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Brillouin spectra have been collected in situ at temperatures up to ∼1000 K for different crystallographic directions from two single crystal plates of LaAlO(3) perovskite. Elastic moduli derived from these, together with heat capacity, spontaneous strain and Raman data from the literature, have then been used to calibrate the coefficients in a classical Landau free energy expansion for the second order [Formula: see text] phase transition at T(c) = 817 K. The static strain/order parameter coupling model provides a quantitative description of elastic softening between room temperature and ∼700 K, but from ∼700 K up to T(c) additional elastic softening correlates with the development of a central peak in the Brillouin spectra. The presence of quasi-elastic scattering, which reaches maximum intensity ∼5-15 K below T(c), implies a strong dynamical component to the phase transition. Relaxation times estimated from the width of the central peak are of the order of ∼10-100 ps and appear to be more or less constant between ∼700 and 800 K, which is consistent with an intrinsic origin associated with phonon density fluctuations. Central peak width variations and an irregular pattern of acoustic velocity variations in a 20 K temperature interval below T(c) are interpreted in terms of flipping of clusters of tilted octahedra between different ⟨111⟩, ⟨011⟩ and ⟨001⟩ tilt axes. The additional softening beyond that expected from the classical strain/order parameter coupling model can be understood in terms of coupling of acoustic modes with the central peak mode(s).

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Section: Introductionmentioning

confidence: 52%

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO₃: II. Mechanisms of static and dynamical softening

Carpenter¹,

Sinogeikin²,

Bass³

2009

J. Phys.: Condens. Matter

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“…[15]). This number is smaller than resembles the behaviour predicted for a soft-phonon dispersion curve in the course of a HT + IC + commensurate phase transition [28]. Finally 4), notwithstanding controversial theoretical work [29,30], the CDW model is also supported by recent first-principle calculations which provide strong evidence for the existence of a .classical Peierls instability, on W(OO1) [31].…”

supporting

confidence: 52%

Evidence for a Charge Density Wave Driven Reconstruction in W(001)

Ernst¹,

Hulpke²,

Toennies³

1989

Europhys. Lett.

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“…λeq 2 . With respect to anomalies of shear elastic constants, the linearquadratic contributions will give a stepwise softening below the transition point (improper ferroelastic or co-elastic), while the bilinear term will give non-linear softening as the transition point is approached from both above and below (pseudoproper ferroelastic) [61][62][63][64]. From figure 2 it is clear that the dominant strain in coarse grained samples is e tx and from figure 7 it is clear that the dominant softening mechanism has the form expected for a pseudoproper ferroelastic transition.…”

Section: Strain/order Parameter Couplingmentioning

confidence: 99%

Strain heterogeneity and magnetoelastic behaviour of nanocrystalline half-doped La, Ca manganite, La_0.5Ca_0.5MnO₃

Pagliari

Dapiaggi

Maglia

et al. 2014

J. Phys.: Condens. Matter

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Elastic and anelastic properties of La0.5Ca0.5MnO3 determined by resonant ultrasound spectroscopy in the frequency range ∼100-1200 kHz have been used to evaluate the role of grain size in determining the competition between ferromagnetism and Jahn-Teller/charge order of manganites which show colossal magneto resistance. At crystallite sizes of ∼75 and ∼135 nm the dominant feature is softening of the shear modulus as the charge order transition point, Tco (∼225 K), is approached from above and below, matching the form of softening seen previously in samples with 'bulk' properties. This is consistent with a bilinear dominant strain/order parameter coupling, which occurs between the tetragonal shear strain and the Jahn-Teller (Γ3(+)) order parameter. At crystallite sizes of ∼34 and ∼42 nm the charge ordered phase is suppressed but there is still softening of the shear modulus, with a minimum near Tco. This indicates that some degree of pseudoproper ferroelastic behaviour is retained. The primary cause of the suppresion of the charge ordered structure in nanocrystalline samples is therefore considered to be due to suppression of macroscopic strain, even though MnO6 octahedra must develop some Jahn-Teller distortions on a local length scale. This mechanism for stabilizing ferromagnetism differs from imposition of either an external magnetic field or a homogeneous external strain field (from a substrate), and is likely to lead both to local strain heterogeneity within the nanocrystallites and to different tilting of octahedra within the orthorhombic structure. An additional first order transition occurs near 40 K in all samples and appears to involve some very small strain contrast between two ferromagnetic structures.

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Optical Studies of Structural Phase Transitions

Cited by 18 publications

References 126 publications

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO₃: II. Mechanisms of static and dynamical softening

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO₃: II. Mechanisms of static and dynamical softening

Evidence for a Charge Density Wave Driven Reconstruction in W(001)

Strain heterogeneity and magnetoelastic behaviour of nanocrystalline half-doped La, Ca manganite, La_0.5Ca_0.5MnO₃

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Optical Studies of Structural Phase Transitions

Cited by 18 publications

References 126 publications

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO3: II. Mechanisms of static and dynamical softening

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO3: II. Mechanisms of static and dynamical softening

Evidence for a Charge Density Wave Driven Reconstruction in W(001)

Strain heterogeneity and magnetoelastic behaviour of nanocrystalline half-doped La, Ca manganite, La0.5Ca0.5MnO3

Contact Info

Product

Resources

About

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO₃: II. Mechanisms of static and dynamical softening

Elastic relaxations associated with the Pm\bar 3 m –R\bar 3 c transition in LaAlO₃: II. Mechanisms of static and dynamical softening

Strain heterogeneity and magnetoelastic behaviour of nanocrystalline half-doped La, Ca manganite, La_0.5Ca_0.5MnO₃