Electronic polarizabilities of ions in doubly refracting crystals

Pohl, Douglas G.

doi:10.1107/s0567739478001217

Cited by 27 publications

(11 citation statements)

References 9 publications

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“…The deviation will be caused by the water molecules which contribute to the mutual polarization within the structure. This interaction can be considered using the computer program DIPSUM of Pohl (1978). For that purpose, the C-atom is assumed to be non-polarizable, and the polarizabilities of Ca and oxygen atoms of the carbonate group are assumed to be 0.42 and 1.43 Â 3 , respectively (Pohl, 1979), and the polarizability of the water molecules is estimated to be 1.47 Â 3 (by means of the Lorentz-Lorenz formula applied to water (Pohl, 1982).…”

Section: Discussionmentioning

confidence: 99%

Refinement of the structure of Ikaite, CaCO₃ - 6H₂O

Hesse¹,

Küppers²,

Suess³

1983

Zeitschrift Für Kristallographie - Crystalline Materials

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Ikaite, CaC0 3 · 6 H 2 0, is monoclinic, C2/c, with a = 8.792(2), b = 8.310(2), c = 11.021(2) Α, β = 110.53(5)°, Ζ = 4. With 2205 independent reflections taken at -25 °C of a naturally grown crystal specimen the structure was refined to a weighted R w = 0.028. The C0 3 group is planar with C-O distances 1.279(2) and 1.290(1) (2 χ) Â. The hydrogen bond network is determined. The optical behaviour is explained by structural characteristics.

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Section: Discussionmentioning

confidence: 99%

Refinement of the structure of Ikaite, CaCO₃ - 6H₂O

Hesse¹,

Küppers²,

Suess³

1983

Zeitschrift Für Kristallographie - Crystalline Materials

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“…Thin Solid Films, 37, L 15-L 16. TSUTSUMI, T. (1970 Recently, a method of determining electronic polarizabilities of ions in crystals has been given by Pohl (1978). If both optical and structural data are available, polarizabilities can be obtained for the ions composing the structure of a doubly refracting crystal.…”

Section: Semiletov S a Imanov R M And Ragimli N A (1976)mentioning

confidence: 99%

Determination of electronic polarizabilities of ions in orthosilicates

Pohl¹,

Eck²,

Klaska³

1978

Acta Cryst Sect A

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“…There are however additional difficulties with every improved model, leading to the conclusion that the problem of too many coefficients and not enough data cannot be easily removed. As pointed out by a number of authors (Spangenberg, 1923;Fajans & Joos, 1924;Born & Heisenberg, 1924;Bragg, 1925;Batsanov, 1966;Pohl, 1978;Pohl, Eck & Klaska, 1978) the polarizability of the anions varies with the size of the cation. Specifically, small cations tend to reduce the polarizability of the anions.…”

mentioning

confidence: 99%

“…The latest studies are those given by Isherwood &James (1976) andPohl (1978). In his paper Pohl (1978) has developed a method to determine the electronic polarizabilities of ions from structural and optical data by a least-squares fit. The method is based on Bragg's (1924) model of point dipoles and on an exact calculation of Lorentz-factor tensors.…”

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confidence: 99%

“…Optical constants are given by Winchell & Winchell (1964). Application of Pohl's (1978) method yields the electronic polariz- Bragg's (1924) ideas, the birefringence arises from the oxygens within the isolated COl-groups: the stronger the birefringence the stronger the influence of the O z-ions on each other. Strengthening of the oxygen interaction can take place in two ways.…”

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confidence: 99%

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Point-dipole theory and optical birefringence of calcite-type carbonates

Pohl¹,

Ram²

1979

Acta Cryst Sect A

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A critical survey of the literature has revealed that recent structure determinations and optical data are available for only three calcite-type carbonates: calcite, rhodochrosite and magnesite. For these structures, the limitations of the pointdipole approximation are discussed.The point-dipole model was introduced by Bragg (1924) to explain quantitatively the birefringence of calcite and aragonite with respect to the crystal structures. In this approach optical anisotropy arises from differences in dipole-dipole coupling along different crystallographic directions. This source of anisotropy is connected with the Lorentz-factor tensor. In addition, however, optical anisotropy may arise from an intrinsic anisotropy in the constituent ions. In this case electronic polarizability tensors should be considered.In order to investigate the relation between atomic arrangement and double refraction, the crystals of carbonates have been used repeatedly. The latest studies are those given by Isherwood &James (1976) andPohl (1978). In his paper Pohl (1978) has developed a method to determine the electronic polarizabilities of ions from structural and optical data by a least-squares fit. The method is based on Bragg's (1924) model of point dipoles and on an exact calculation of Lorentz-factor tensors. This model satisfactorily accounts for the double refraction of aragonite-type carbonates. In the present paper we discuss the application of the method to calcite-type carbonates.Structural parameters of only three calcite-type carbonates have been determined: calcite (Chessin, Hamilton & Post, 1965), rhodochrosite (Brown & Forsyth, 1967) and magnesite (Oh, Morikawa, Iwai & Aoki, 1973). Optical constants are given by Winchell & Winchell (1964). Application of Pohl's (1978) method yields the electronic polariz- Bragg's (1924) ideas, the birefringence arises from the oxygens within the isolated COl-groups: the stronger the birefringence the stronger the influence of the O z-ions on each other. Strengthening of the oxygen interaction can take place in two ways. Firstly, the distance between the carbon and oxygen can be diminished. Secondly, the polarizability of the oxygen ion can be increased. Since the C-O distance is fixed according to the structure determination, only an increased polarizability of the 0 2-ion remains. However, this results in an increased mean refractivity which in return is compensated by a smaller polarizability of the cation, thus explaining the above results.To overcome the shortcomings encountered with the Bragg model of point dipoles, two improvements may be considered. Firstly, the point dipoles can be positioned outside the atomic centers, because the outer electrons responsible for the optical effects may have a center of gravity distinct from that determined by X-rays. Secondly, an intrinsic anisotropy can be allocated to the polarizability of the ions. Both of these improvements involve the introcluction of at least one extra parameter. Thus the number of adjustable parameters will exce...

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Electronic polarizabilities of ions in doubly refracting crystals

Cited by 27 publications

References 9 publications

Refinement of the structure of Ikaite, CaCO₃ - 6H₂O

Refinement of the structure of Ikaite, CaCO₃ - 6H₂O

Determination of electronic polarizabilities of ions in orthosilicates

Point-dipole theory and optical birefringence of calcite-type carbonates

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Electronic polarizabilities of ions in doubly refracting crystals

Cited by 27 publications

References 9 publications

Refinement of the structure of Ikaite, CaCO3 - 6H2O

Refinement of the structure of Ikaite, CaCO3 - 6H2O

Determination of electronic polarizabilities of ions in orthosilicates

Point-dipole theory and optical birefringence of calcite-type carbonates

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Product

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Refinement of the structure of Ikaite, CaCO₃ - 6H₂O

Refinement of the structure of Ikaite, CaCO₃ - 6H₂O