Behaviour of iron, cobalt and nickel fluosilicate hehahydrates under pressure

Asadov, S. K.; Zavadskii, E. A.; Kamenev, V. I.; Kamenev, K. V.; Todris, B. M.

doi:10.1016/0921-4526(92)90561-6

Cited by 8 publications

(9 citation statements)

References 8 publications

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“…A thermodynamic cycle using two isobars and two isotherms would then show one anomaly for each of the upper transition lines, depending on direction, but two for the lower ones, which thus could be mistaken as second order transitions. 5[(x-3.4)(x-1.9)+31+0.03/(x-0.4) Fig.4 shows a section of the P-T diagram of CoSiF 6(6H 2 0 ) [5], where the L -line suggests an V-type asymptotic behaviour; a critical point might exist for p < 0 as the lability lines approach each other; eventual transitions below the asymptote T k are not presented. The Ephase is a modified R3-phase under conservation of the threefold axis; indeed, E and R3 are only discriminated from each other by a break in the slope of the lattice plane distance d 440 ( T) [5].…”

Section: = 2p(p-p T)(t -T 2)(t -T 3 ) = 3cy(t-t T ) -(F32 -3 Co)(t -Tmentioning

confidence: 91%

“…5[(x-3.4)(x-1.9)+31+0.03/(x-0.4) Fig.4 shows a section of the P-T diagram of CoSiF 6(6H 2 0 ) [5], where the L -line suggests an V-type asymptotic behaviour; a critical point might exist for p < 0 as the lability lines approach each other; eventual transitions below the asymptote T k are not presented. The Ephase is a modified R3-phase under conservation of the threefold axis; indeed, E and R3 are only discriminated from each other by a break in the slope of the lattice plane distance d 440 ( T) [5]. Ignoring this small difference, such a diagram can be easily constructed using expansions up to a quadratic term (inset).…”

Section: = 2p(p-p T)(t -T 2)(t -T 3 ) = 3cy(t-t T ) -(F32 -3 Co)(t -Tmentioning

confidence: 91%

“…Fig. 6 a, in particular, shows a pair of transition lines above and below a T-asymptote in the P-T diagram of FeSiF 6(6H2 0 ) [5]. The reconstruction (Fig.…”

Section: Examplesmentioning

confidence: 97%

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Phase Diagrams with Asymptotic Transition Lines

Dunkel

Bärner

Zavadskii

1997

Ber Bunsenges Phys Chem

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While linear and curved phase transition lines in P(T) or H(T) diagrams can be described by adding linear and quadratic terms in a joint expansion of the Landau coefficients a, b in terms of P-P, and T-T, where (PI' T t ) is a critical point, a new class of phase diagram is obtained by allowing for bilinear, e(P-Pt)(T-T t), and higher product terms. In this contribution we relate these new expansion terms to some hitherto unexplained experimental P-T and H-T phase diagrams.(1) while the sufficient condition (minimum) is:we have a turnover from second to first order at T, and (Pt, Tt) therefore defines a critical point. Generally, for first order transitions a hysteresis and with it lability lines appear. In the Landau approach these result as follows: the necessary condition for equilibrium of a system which follows Eq. (1) is:(5) (T-T t) +15(T-T t )2 b = (J(T-T t )phase transition lines are contained in the Landau coefficients a, band c. (1) describes the competition between a disordered (say, paramagnetic, "pm") state and an ordered (say, ferromagnetic, "fm") state. In the pm state, the order parameter is " = 0; in that case Eq. (3) is always fulfilled, but Eq. (4) only as long as a>O. Thus, if we have a zero crossing of a(P, T), i.e. a = 0, the stable pm state (minimum) transforms into an unstable pm state (maximum). Consequently, the fm state will now appear and with it ,,>0. ,,(P, T»O can be obtained from letting the bracket in Eq, (3) go to zero as n » 0 but condition (3) has to be fulfilled. For a first order transition, b < 0, in particular one obtains: FundamentalsWhen one considers pressure-and temperature-dependent phase transitions in the framework of the Landau theory, in a first step one writes the thermodynamic potential rp as a function of the order parameter n: rp = a,,2 + bn" + en"

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Section: = 2p(p-p T)(t -T 2)(t -T 3 ) = 3cy(t-t T ) -(F32 -3 Co)(t -Tmentioning

confidence: 91%

Section: = 2p(p-p T)(t -T 2)(t -T 3 ) = 3cy(t-t T ) -(F32 -3 Co)(t -Tmentioning

confidence: 91%

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Phase Diagrams with Asymptotic Transition Lines

Dunkel

Bärner

Zavadskii

1997

Ber Bunsenges Phys Chem

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“…During the last several decades, single crystals of NiSiF 6 ·6H 2 O have been discussed by a number of experimental techniques, such as electron paramagnetic resonance [1][2][3][4][5][6][7][8][9], paramagnetic relaxation [10], optical absorption [11][12][13], nuclear magnetic resonance [14][15][16] and Xray diffraction [17]. Because the determination of local structure is meaningful and helpful for a good insight into the property, in order to clearly comprehend the characteristics of transitionmetal complex molecules, it is necessary to establish the inter-relationships between electronic and molecular structures.…”

Section: Introductionmentioning

confidence: 99%

Comparative analysis of the difference of local structure between EPR theory and X-ray diffraction experiment for NiSiF6·6H2O crystal

Wang¹,

Kuang²,

Li³

et al. 2009

Journal of Alloys and Compounds

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“…It is connected with a second-order phase transition manifested near 220 K, at which the crystal constant reveals anomalous behavior asa function of temperature at various pressures [8].…”

Section: Introductionmentioning

confidence: 99%

Zero-field splitting in NiSiF6−6H2O and its pressure, stress and temperature dependences: A supplementary study

Krupski

Krupska

2003

Appl. Magn. Reson.

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The zero-field splitting in NiSiF 6 . 6H20 was studied as a function of hydrostatic pressure and uniaxiaI stress at temperatures above and below 220 K, at which the crystaI exhibits a secondorder phase transition. The anisotropy of the thermal expansion coefficients parallel and perpendicular to the trigonal symmetry axis was measured in a wide range of temperatures. On the basis of the 0btained data the spin-phonon interaction has been separated from the thermal expansion of the crystal. At high and low temperatures the two contributions have opposite signs and exhibit much higher values above 220 K than below this temperature. This is explained by the high anisotropy of the thermal expansion of the erystal characteristic of the high-temperature phase.

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Behaviour of iron, cobalt and nickel fluosilicate hehahydrates under pressure

Cited by 8 publications

References 8 publications

Phase Diagrams with Asymptotic Transition Lines

Phase Diagrams with Asymptotic Transition Lines

Comparative analysis of the difference of local structure between EPR theory and X-ray diffraction experiment for NiSiF6·6H2O crystal

Zero-field splitting in NiSiF6−6H2O and its pressure, stress and temperature dependences: A supplementary study

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