Thermal properties and phase transitions in (NH4)3ZrF7

Fokina, V. D.; Горев, М. В.; Bogdanov, E. V.; Pogorel’tsev, E. I.; Flerov, I. N.; Laptash, N. M.

doi:10.1016/j.jfluchem.2013.07.001

Cited by 18 publications

(28 citation statements)

References 18 publications

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“…It should be noted that the enthalpy value ∆H 1-2 for elpasolite is comparable to the total enthalpy Σ∆H i = 3000 J mol -1 determined by the same DSM method for cryolite (NH 4 ) 3 ZrF 7 undergoing six structural transformations [19]. However, the total entropy changes differ for both fluoride compounds significantly: ∆S 1-2 = Rln2.6 and Σ∆S i = Rln6.…”

Section: Resultssupporting

confidence: 60%

“…. It was also found that the cubic phase in the elpasolite (NH 4 ) 2 KZrF 7 is less stable since the first phase transition occurs ~ 40 K higher than in cryolite [19].…”

Section: Resultsmentioning

confidence: 99%

“…Rln6, (Hf) Rln4 [19,20]. However, the change in entropy at each of the transformations was turned out to be significantly less than Rln2.…”

Section: Introductionmentioning

confidence: 94%

“…More recent comprehensive studies revealed that ammonium zirconium and hafnium cryolites undergo a more complex sequence of structural distortions [18][19][20][21]. Careful polarization-optical, X-ray, calorimetric and Raman investigations as well as the group-theoretical analysis have shown that (NH 4 ) 3 ZrF 7 and (NH 4 ) 3 HfF 7…”

Section: Introductionmentioning

confidence: 99%

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Structural, thermal and optical properties of elpasolite-like (NH4)2KZrF7

Pogorel’tsev

Melnikova

Мolokeev

et al. 2019

Journal of Solid State Chemistry

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New fluoride compound (NH 4) 2 KZrF 7 with the elpasolite structure (sp. gr. Fm-3m) was synthesized by partial cationic substitution in (NH 4) 3 ZrF 7 cryolite. Due to small difference in ionic radii of K + and NH 4 + , non-equivalent crystallographic positions 8c and 4b are occupied by both cations. Investigations of thermal, optical and structural properties in a wide range of temperature revealed two phase transitions Fm-3m ↔ P4 2 /ncm ↔ P4 2 /nmc of the first order. The results obtained are discussed in comparison with the data for the previously studied related cryolite (NH 4) 3 ZrF 7 .

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Section: Resultssupporting

confidence: 60%

“…. It was also found that the cubic phase in the elpasolite (NH 4 ) 2 KZrF 7 is less stable since the first phase transition occurs ~ 40 K higher than in cryolite [19].…”

Section: Resultsmentioning

confidence: 99%

“…Rln6, (Hf) Rln4 [19,20]. However, the change in entropy at each of the transformations was turned out to be significantly less than Rln2.…”

Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Structural, thermal and optical properties of elpasolite-like (NH4)2KZrF7

Pogorel’tsev

Melnikova

Мolokeev

et al. 2019

Journal of Solid State Chemistry

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“…К таковым, в частности, относятся Zr, Hf, Nb, Ta, для которых известны шести-, семи-и восьмикоординированные ани-онные полиэдры. Несмотря на сравнительно широкий круг публикаций, посвященных синтезу и исследованию такого рода соединений [6][7][8][9][10][11][12][13][14][15], отсутствует системати-ческое изучение влияния структурных особенностей на термодинамическую устойчивость кристаллических фаз и физические свойства.…”

Section: Introductionunclassified

Тепловые, оптические и диэлектрические свойства Rb-=SUB=-2-=/SUB=-TaF-=SUB=-7-=/SUB=-

Погорельцев¹,

Мельникова²,

Карташев³

et al. 2017

Физика Твердого Тела

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Выполнены исследования теплофизических, оптических и диэлектрических свойств Rb 2 TaF7. Изменение химического давления во фторидах A + 2 TaF7 за счет катионного замещения аммония рубидием не по-влияло на сегнетоэластическую природу структурных искажений, но привело к стабилизации высоко-и низкотемпературной фаз и к росту двулучепреломления. Энтропия фазового перехода P4/nmm ↔ Cmma характерна для превращений типа смещения, что согласуется с моделью структур исходной и искаженной фаз. Анизотропия химического давления является причиной изменения знаков аномальной деформации и барического коэффициента dT /d p для Rb 2 TaF7 по сравнению с наблюдаемыми для аммонийного аналога.Исследование выполнено при финансовой поддержке РФФИ и правительства Красноярского края в рамках научного проекта № 16-42-243001.

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