Evolution of order-disorder phase transitions in the mixed system KCNx: KCl1-x: I. Dielectric studies

Julian, Michael; Lüty, Fritz

doi:10.1080/00150197708237158

Cited by 46 publications

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“…For a mixed crystal with a concentration x = 0.02, no loss peaks were observed down to 1.5 K. 5.2.5.3. Dielectric relaxation at higher concentrations A detailed and systematic investigation of the dielectric properties of (KC1)~_x(KCN)x and (KBr)l x(KCN)x mixed crystals has been reported by Ltity and co-workers (Julian andLfity 1977, Ltity 1981). Subsequently, 5(e), T) data have been reported by Knorr and Loidl (1982), Loidl et al (1982), Bhattacharya et al (1982), Lfity and Ortiz-Lopez (1983), Ortiz-Lopez (1983), Birge et al (1984) and B6hmer (1985).…”

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confidence: 93%

Orientational glasses

Höchli

Knorr

Loidl

1990

Advances in Physics

730

369

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This review summarizes experimental evidence for the freezing of reorienting moments in solids. The moments may be of dipolar or quadrupolar nature, or both; they belong to one of the constituents of a mixed-crystal solid. Extensive results are reported for the following systems: KC1 doped with hydroxyl, potassium tantalate doped with Li, Na and Nb, alkali halide cyanides and alkali-alkali cyanides, rubidium ammonium dihydrogen phosphate, solid ortho-para hydrogen and argon-nitrogen mixtures. These have clearly glass-like properties. In other systems, results are limited to one or two methods hinting at glass formation; some of those are also reported. Clustering phenomena and the slow-down of reorientations at the freezing temperature are observed in susceptibility measurements and by local probing on nuclear spins. The modulation of the structure by cluster formation is revealed by diffraction experiments. These phenomena are confronted with model predictions and numerical simulations. l , 2. IntroductionWe apply the term 'orientational glass' to a solid consisting of a regular lattice some of whose sites are occupied by constituents containing a dipole or quadrupole moment. These moments have orientational degrees o f freedom; they interact with one another and, below some freezing temperature Tf, their motion slows and they freeze into a configuration devoid of long-range order. A typical example is KC1 doped with OH molecules that replace C1 at random sites. At ! 0 K the dipoles associated with the OH molecules reorient rapidly, whereas at 0-1 K their orientations are static on experimental time scales, yet there is no macroscopic (spontaneous) polarization. Early investigations of this orientational-glass prototype (of the subspecies 'dipole glass') were performed by Kfinzig et al. (1964). Brout (1965)considered its short-range order and pointed out the analogy with what was to become the spin-glass prototype, Cu doped with Mn, where Mn has a spin of ~ and therefore contains magnetic degrees of freedom.The use of the word 'glass' suggests a similarity with what we call ~canonical glasses' (the prototype of which is fused silica, SiO2), in order to distinguish them from orientational and spin glasses. There are indeed orientational degrees of freedom in SiO2, in addition to rapid freezing of the moments and a low-temperature configuration devoid of order. Owing to the lack of an underlying lattice, however, it is impossible to associate moments at site i with interactions between moments at sites i and j, which is a pre-requisite for modelling a glass in terms of a Hamiltonian.Spin-glass models are based almost entirely on the existence of a Hamiltonian containing interactions between spins and their coupling to a magnetic field. The interactions chosen to model spin glasses are, in general, totally unspecific for spins. They are usually probabilistic distributions o f interaction strengths with a variance Var~j much larger than their average ~j and with both quantities independent of i j. The picture of spi...

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confidence: 93%

Orientational glasses

Höchli

Knorr

Loidl

1990

Advances in Physics

730

369

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“…Crudely speak ing, the molecular ions in that type of crystals play a role of " molecular grease" , lowering the re sponse of the crystal to shear strain. This role is evident from experiments with doped crystals K C 1: K C N , where a decrease of the sound velocity by an appreciable amount has been found [3] as a consequence of doping.…”

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confidence: 68%

Role of translational-rotational coupling in lattice dynamics and ferroelastic phase transitions; the s-triazine crystal

Luty¹,

Avoird²

1984

Chemical Physics

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An analysis of the lattice dynamics for low-and high-temperature phases of s-triazine crystals is presented. Special attention is paid to the problem of translational-rotational coupling as a driving force for the structural phase transition. Results of numerical calculations for static and dynamical properties are used to predict parameters of the Landau free-energy expansion for the crystal. Finally, recent theories of the ferroelastic phase transition in the s-triazine crystal are critically discussed.

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Etude des Spectres de Diffusion Raman Et d'Absorption Infrarouge des Cyanures de Sodium et de Potassium En Phase II et Phase III

Fontaine

1980

J Raman Spectroscopy

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The infrared and Raman spectra of potassium and sodium cyanides have been recorded in the two orthorhomhic phases (Ising spin disordered phase I1 and ordered phase 111). By comparing the intensity of the modes we show that the two crystals have a different behaviour, though they belong to the same space group. In particular, the two librational modes in phase I1 are accidentally degenerate in KCN (a = 116 Em-' at T = 150 K), while they are widely separated in NaCN (u = 218 cm-' and 104 cm-' at T = 250 K). In KCN the second mode seems due to the disorder. Some possible attributions for the translatory motions in phase I11 are given, based on coupling with the librational motions.ou deux unitts formulaires par maille primitive, selon la phase CtudiCe) ainsi que I'Ctendue en temDCrature de INTRODUCTION ieurs phases disorddnnkes en font de bons sujets expCrimentaux et thCoriques.Sous pression normale, on dCnombre trois phases diffCrentes:Connus depuis le dCbut de ce sikcle, les cristaux de cyanure de sodium et de potassium ont toujours prisentk un grand intkrst dans les Ctudes des phases dCsordonnCes. E n effet, leur simplicit6 structurelle (une KCN NaCN Phase I (plastique) 168,3 K < T < Tf,,,,, = 907,6 K 283,7 K < T < Tfusion = 836,s K Phase I1 (dCsordre de spin) 171,9K< T<283,7 K Phase I11 (ordonnCe) T < 82,9 K T < 171,9 K 82,9 K < T < 168,3 K Nous n'ktudierons que les phases I1 et I11 (pour 1'Ctude de la phase plastique par diffusion Raman voir notamment RCf. 14).La mise en ordre des ions CN-dans les cyanures de sodium et de potassium se fait en deux Ctapes: une mise en ordre suivant une seule direction (dksordre de spin de type 'spin d'Ising': phase 11), puis une mise en ordre complet (phase 111).La phase I1 a CtC CtudiCe par diffCrentes mCthodes expkrimentales: -diffraction de rayons X, ce qui a permis B Bijvoet et ~1 . l .~ d'en dtterminer la structure: D;i(Immm) avec une unit6 formulaire par maille primitive (2 = 1); -1es mesures de chaleur spkcifique par Matsuo et al.; 334 -1es mesures de pertes diklectriques par Julian et -la diffusion Raman et l'absorption infrarouge: Dultz et aL6 et F~n t a i n e .~. 'La phase I11 n'a tout d'abord CtC mise en Cvidence que par les mesures de chaleur sp6cifique 334 puis par mesure de 1'Cvolution des raies de rCsonance magnktique nuclCaire (Fukushima'), ainsi que par diffusion Raman (Winchester' et nous-rnsmes'). Nous avons pu pricker, en supposant, d'aprks les mesures de chaleur spkcifique, que le changement de phase Ctait du second ordre, que le Luty;'O groupe d'espace de la maille cristallographique Ctait D;: avec deux unites formulaires par maille primitive. Ce rksultat a CtC v&rifi6 par diffraction de neutrons sur poudre, successivement par nous-msmes" pour NaCN puis par Rowe et a1.I2 pour NaCN et KCN.Dans cette structure le site de tous les atomes est C2", si bien que les cations, ainsi que le centre de gravitC des ions cyanures ne sont plus sur des sites centrCs comme cela Ctait le cas dans la phase 11. Par ailleurs, cette structure, dont les paramktres de la maille so...

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Evolution of order-disorder phase transitions in the mixed system KCN_x: KCl_1-x: I. Dielectric studies

Cited by 46 publications

References 6 publications

Orientational glasses

Orientational glasses

Role of translational-rotational coupling in lattice dynamics and ferroelastic phase transitions; the s-triazine crystal

Etude des Spectres de Diffusion Raman Et d'Absorption Infrarouge des Cyanures de Sodium et de Potassium En Phase II et Phase III

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