Soft modes and elastic strain at the tetragonal-to-monoclinic phase transition in antifluorite and related structure types

Ihringer, J.; Abrahams, S. C.

doi:10.1103/physrevb.30.6540

Cited by 21 publications

(11 citation statements)

References 34 publications

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“…The /n, it has been pointed out that to lowest order the monoclinic angle may be forced to be 90°due to mode coupling between rotational modes of the MX octahedra (10). In (ND ) PdCl , however, it appears that the transition pathway occurs in one stage to the monoclinic space group from Fm3 m.…”

Section: Figmentioning

confidence: 96%

“…The relationship between the various instabilities in the ammonium antifluorites, the size of the unit cell, and the composition of the MX unit has been discussed recently by Zhang et al (9). There is some suggestion that transitions additional to those predicted from group-subgroup relationships can be generated in these systems, provided that the transition can happen continuously (the nondisruptive criterion) (10,11). This may explain some unusual increases in symmetry at low temperatures in certain antifluorites with more than one transition (11,12).…”

Section: Introductionmentioning

confidence: 93%

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The Phases of the Antifluorite Deuterated-Ammonium Palladium Hexachloride, (ND4)2PdCl6

Swainson

Powell

Weir

1997

Journal of Solid State Chemistry

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Section: Figmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 93%

The Phases of the Antifluorite Deuterated-Ammonium Palladium Hexachloride, (ND4)2PdCl6

Swainson

Powell

Weir

1997

Journal of Solid State Chemistry

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“…, has been widely reported 39,40,41,42 . An inverse DM interaction of the type € P i ∝ (r 12 × S 1 × S 2 ) i between spins at locations 1 and 2, separated by a vector r 12 is observed to give rise to a polarization P i in spin cycloidal ferroelectrics such as TbMnO 3 , DyMnO 3 , Ni 3 V 2 O 8 ,…”

Section: And Literature Measurements In Antidistorted Perovskitesmentioning

confidence: 99%

Rotation-reversal symmetries in crystals and handed structures

Gopalan

Литвин

2011

Nature Mater

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Symmetry is a powerful framework to perceive and predict the physical world. The structure of materials is described by a combination of rotations, rotation-inversions and translational symmetries. By recognizing the reversal of static structural rotations between clockwise and counterclockwise directions as a distinct symmetry operation, here we show that there are many more structural symmetries than are currently recognized in right- or left-handed helices, spirals, and in antidistorted structures composed equally of rotations of both handedness. For example, we show that many antidistorted perovskites possess twice the number of symmetry elements as conventionally identified. These new 'roto' symmetries predict new forms for 'roto' properties that relate to static rotations, such as rotoelectricity, piezorotation, and rotomagnetism. They enable a symmetry-based search for new phenomena, such as multiferroicity involving a coupling of spins, electric polarization and static rotations. This work is relevant to structure-property relationships in all materials and structures with static rotations.

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“…Consequently, these AX6E species (E = lone pair of electrons) were considered to be exceptions to the valence shell electron pair repulsion (VSEPR) rules. 3 More recent papers distinguish between dynamically distorted species ("regular octahedra") and statically distorted species with respect to the symmetry of the crystal field and its influence on the phonon-electron (vibronic) coupling.4-6 For compounds A Z SeX 6 and A z TeY 6 (with A=K+, NH 4 +, Rb+. Cs+; X=Cl-, Be; Y=Cl-, Br -, I -), the high -temperature phases show the cubic K z PtCl 6 -type structure (Fig.…”

Section: Introductionmentioning

confidence: 99%

The phase transitions of ferroelastic K2SeBr6: A calorimetric and x-ray diffraction study

Abriel

White

1990

The Journal of Chemical Physics

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Guinier x-ray powder diffraction data in the temperature range from T = 10 to 290 K, and heat capacity measurements from T = 40 to 280 K indicate three phases for K z SeBr 6 . The high-temperature cubic structure [K 2 PtCI 6 -type, space group Fm3m; a = 10.4211 (7) A at T= 290 K] transforms at 237.8 ± 0.3 K with t::.Str = (1.36 ± 0.02) J K -I mol-I to a tetragonal phase with a Rb 2 TeI 6 -type structure [space group P4lmnc; a = 7.313(1) A, c = 10.474(2) A at T= 220 K). A second phase transition at 215 ± 1 K [t::.Str = (0.54 ± 0.01) J K -1 mol-l] results in a monoclinic phase with a K2 TeBr6 -type structure [space group P2 1 /n; a = 7.265(3) A, b = 7.265(3) A. c = 10.438(4) A. P = 89.66(5)" at T= 80 KJ. Both transitions can be interpreted in terms of softening of rotary phonons at the X edge of the Brillouin zone. From the thermal parameters of a single crystal xray structure determination at T = 293 K, this low-temperature instability can be predicted. The results agree with comparable data offerroelastic K2 TeBr6 and refute some earlier speculations concerning the phase transitions in K2 SeBr 6' J FIG. 1. K, ptel. structure. Small spheres are K, octahedra are Ptel. (SeBr. ). J. Chern. Phys. 93 (11).

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Soft modes and elastic strain at the tetragonal-to-monoclinic phase transition in antifluorite and related structure types

Cited by 21 publications

References 34 publications

The Phases of the Antifluorite Deuterated-Ammonium Palladium Hexachloride, (ND4)2PdCl6

The Phases of the Antifluorite Deuterated-Ammonium Palladium Hexachloride, (ND4)2PdCl6

Rotation-reversal symmetries in crystals and handed structures

The phase transitions of ferroelastic K2SeBr6: A calorimetric and x-ray diffraction study

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