Induced and spontaneous optical activity in Pb5Ge3O11single crystals

Koňák, Čestmı́r; Fousek, J.; Kürsten, H. D.

doi:10.1080/00150197808237260

Cited by 20 publications

(3 citation statements)

References 8 publications

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“…One can see (figure 3) that the dependence of optical rotation close to T c is well fitted by the function (T c − T ) μ , where μ = 0.5. Thus, equation ( 20 interval between room temperature and T = T c − 3 K [22]. It is interesting that we observe a tail of optical activity above T c − 5 K and the dependence of optical activity on (T c − T ) 0.5 still remains linear below T < T c − 40 K, though the slope is then changed.…”

Section: Electrogyrationmentioning

confidence: 67%

Electrogyration and Faraday rotation in pure and Cr-doped lead germanate crystals

Adamenko

Klymiv

Duda

et al. 2008

J. Phys.: Condens. Matter

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We present the results of studies on the temperature dependence of the electrogyration (EG) effect, Faraday rotation and natural optical activity in Pb5Ge3O11 and Pb5Ge3O11:Cr crystals at the phase transition. A high EG coefficient is found for Pb5Ge3O11:Cr crystals. We demonstrate how the Curie–Weiss constant, the critical exponents of the order parameter and the dielectric permittivity in Pb5Ge3O11:Cr crystals, as well as the coefficients of thermodynamic potential, could be derived from the temperature dependences of optical activity and the EG coefficient. We also show that the increment of the Faraday rotation in Pb5Ge3O11 and Pb5Ge3O11:Cr crystals appearing at the phase transition is caused by a combined magneto-electrooptic effect induced by spontaneous polarization. It is proportional to the square of spontaneous polarization. The phenomenon revealed by us corresponds to combined effects of crystal optics, which appear due to the common action of different fields.

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Section: Electrogyrationmentioning

confidence: 67%

Electrogyration and Faraday rotation in pure and Cr-doped lead germanate crystals

Adamenko

Klymiv

Duda

et al. 2008

J. Phys.: Condens. Matter

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“…The presence of a hysteresis loop in the natural optical activity measurements can be associated with the gyrotropic order associated with the P 3 space group [24,25], which can indeed be associated with optically active polar domains. Furthermore, the linear electrogyration [4] coefficient of PGO is among the largest ever recorded, with a value γ 33 =(3.1 ± 0.3) × 10 −11 m/V near 450 K in chromium doped conditions (0.8 %) [25][26][27][28]. Another intriguing aspect of PGO involves its ferroelectric domain walls (DWs).…”

Section: Introductionmentioning

confidence: 99%

Ferroelectricity and chirality in the Pb5Ge3O11 crystal

Fava,

Lafargue-Dit-Hauret,

Romero

et al. 2024

Phys. Rev. B

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We study from first-principles calculations the ferroelectric structural phase transition of Pb 5 Ge 3 O 11 crystal. The calculations of phonons and Born effective charges of the paraelectric phase allow us to identify a polar instability that is unstable in both transverse-optic and longitudinal-optic versions, giving rise to an entire branch of instability along a propagation vector parallel to the mode polarization (the hexagonal axe). This is the hint of hyperferroelectricity and the stable head-to-head and tail-to-tail domain, as recently reported from both experiments and theory. Then, our analysis of the ferroelectric phase shows that the polarization of Pb 5 Ge 3 O 11 is uniaxial along the hexagonal axes and with small in-plane components due to a piezoelectric effect. The symmetry-adapted mode analysis shows that the total ferroelectric ground state distortion comes mainly from polar distortions of the unstable polar phonon mode but also from an invariant, cooperative mode that amplifies the polar distortion. We also build a phenomenological model that highlights how the coupling between these modes is at play and helps us understand how to reproduce the second-order phase transition. At last, we also quantify the structural chirality through the continuous symmetry measure method and trace its origin to the polar unstable mode itself. By extending our approach to the phonon states we further clarify why the final ground state distortion is more chiral than the unstable polar mode responsible for the symmetry lowering. Finally we study the phonon angular momentum (AM) distribution in both phases and identify trends in the AM behaviour across the Brillouin zone.

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“…In 1972, Iwasaki et al [1] analyzed the experimental dependence 𝑃 S = 𝑃 S (𝑇) for the PGO crystals and found that its behavior corresponds to the classical Landau theory [i.e., 𝑃 S ∝ (𝑇 C − 𝑇) 0.5 ] only in the region 𝑇 C −𝑇 < 30 K below the point 𝑇 C = 450 K. Further on, Konak et al [10] noted that the temperature dependence of the optical rotation 𝜌 in PGO is described by the "empirical" relation 𝜌 ∝ (𝑇 C − 𝑇) 0.35 in the region 𝑇 C − 𝑇 > 3 K (with 𝑇 C = 450 K). In other words, although 𝜌 represents a secondary order parameter of the PT, its behavior differs significantly from that predicted by the Landau theory.…”

Section: Introductionmentioning

confidence: 99%

Critical exponents of the order parameter of diffuse ferroelectric phase transitions in the solid solutions based on lead germanate: studies of optical rotation

Adamenko¹,

Vlokh²

2022

Condens. Matter Phys.

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In this work we show that the critical exponents of the order parameter (CEOPs) of diffuse ferroelectric phase transitions (DFEPTs) occurring in lead germanate-based crystals can be determined using experimental temperature dependences of their optical rotation. We also describe the approach that suggests dividing a crystal sample into many homogeneous unit cells, each of which is characterized by a non-diffuse phase transition with a specific local Curie temperature. Using this approach, the CEOPs have been determined for the pure Pb5Ge3O11 crystals, the solid solutions Pb5(Ge1-xSix)3O11 (x = 0.03, 0.05, 0.10, 0.20, 0.40) and (Pb1-xBax)5Ge3O11 (x = 0.02, 0.05), and the doped crystals Pb5Ge3O11:Li3+ (0.005 wt.), Pb5Ge3O11:La3+ (0.02 wt.), Pb5Ge3O11:Eu3+ (0.021 wt.), Pb5Ge3O11:Li3+, Bi3+ (0.152 wt.) and Pb5Ge3O11:Cu2+ (0.14 wt.). Comparison of our approach with the other techniques used for determining the Curie temperatures and the CEOPs of DFEPTs testifies to its essential advantages.

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Induced and spontaneous optical activity in Pb₅Ge₃O₁₁single crystals

Cited by 20 publications

References 8 publications

Electrogyration and Faraday rotation in pure and Cr-doped lead germanate crystals

Electrogyration and Faraday rotation in pure and Cr-doped lead germanate crystals

Ferroelectricity and chirality in the Pb5Ge3O11 crystal

Critical exponents of the order parameter of diffuse ferroelectric phase transitions in the solid solutions based on lead germanate: studies of optical rotation

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