The Cubic/Tetragonal Phase Transition in D3C–THF: an Optical and X-ray Powder Diffraction Study

Different types of ordering phenomena may occur during phase transitions, described within the universal framework of the Landau theory through the evolution of one, or several, symmetry-breaking order parameter . In addition, many systems undergo phase transitions related to an electronic instability, in the absence of a symmetry-breaking and eventually described through the evolution of a totally symmetric order parameter q linearly coupled to volume change. Analyzing the coupling of a non-symmetry-breaking electronic instability, responsible for volume strain, to symmetry-breaking phenomena is of importance for many systems in nature and here we show that the symmetry-allowed q 2 coupling plays a central role.We use as case study the rubidium manganese hexacyanoferrate Prussian blue analogue, exhibiting phase transitions with hysteresis that may exceed 100 K, and based on intermetallic charge transfer (CT). During the phase transition, the intermetallic CT described through the evolution of q is coupled to cubic-tetragonal ferroelastic symmetry-breaking described through the evolution of . In this system, the symmetry-breaking and non-symmetry breaking deformations have similar amplitudes but the large volume strain is mainly due to CT. We analyze both the ferroelastic and the CT features of the phase transition within the frame of the Landau theory, taking into account the q 2 coupling, stabilizing concomitant CT and Jahn-Teller distortion. The results show that the phase transition and its wide thermal hysteresis originate from the coupling between both processes and that the elastic coupling of each order parameter with the volume strain is responsible for the q 2 coupling. The phase diagrams obtained with this model are in good qualitative agreement with various experimental findings and apply to diverse families of materials undergoing Mott transition, spin-crossover, neutral-ionic transition…, for which isostructural electronic instability driving volume strain can couple to symmetry-breaking or not, create phase transition lines and drive cooperative phenomena.

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“…We decompose the total volume strain 𝑣 𝑠 in sb and nsb components, as done for the symmetricallysimilar cases of leucite and D3C-THF, 35,53 with…”

Section: Landau Analysis Of the Phase Transition A Landau Development...mentioning

confidence: 99%

Landau theory for non-symmetry-breaking electronic instability coupled to symmetry-breaking order parameter applied to Prussian blue analog

et al. 2020

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“…Therefore, an average structure of the cubic and tetragonal chibaite was refined by the Rietveld method 25 . Two structural models with space group symmetry Fd3 _ or I4 1 /a were used because they are reported as space groups of room-temperature phases of MTN-type clathrasil 7,26,27 . Although there are other possible tetragonal space groups for MTN-type clathrasil 26,28 , I4 1 /a is the highest symmetry space group belonging to the Laue group I4/m.…”

Section: Localitymentioning

confidence: 99%

New silica clathrate minerals that are isostructural with natural gas hydrates

Momma

Ikeda

Nishikubo³

et al. 2011

Nat Commun

131

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silica clathrate compounds (clathrasils) and clathrate hydrates are structurally analogous because both materials have framework structures with cage-like voids occupied by guest species. The following three structural types of clathrate hydrates are recognized in nature: cubic structure I (sI); cubic structure II (sII); and hexagonal structure H (sH). In contrast, only one naturally occurring silica clathrate mineral, melanophlogite (sI-type framework), has been found to date. Here, we report the discovery of two new silica clathrate minerals that are isostructural with sII and sH hydrates and contain hydrocarbon gases. Geological and mineralogical observations show that these silica clathrate minerals are traces of lowtemperature hydrothermal systems at convergent plate margins, which are the sources of thermogenic natural gas hydrates. Given the widespread occurrence of submarine hydrocarbon seeps, silica clathrate minerals are likely to be found in a wide range of marine sediments.

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Structural Distortions and Modulations in Microporous Materials

Depmeier

1999

Molecular Sieves

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The Cubic/Tetragonal Phase Transition in D3C–THF: an Optical and X-ray Powder Diffraction Study

Cited by 5 publications

References 17 publications

Landau theory for non-symmetry-breaking electronic instability coupled to symmetry-breaking order parameter applied to Prussian blue analog

Landau theory for non-symmetry-breaking electronic instability coupled to symmetry-breaking order parameter applied to Prussian blue analog

New silica clathrate minerals that are isostructural with natural gas hydrates

Structural Distortions and Modulations in Microporous Materials

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