High temperature phase transitions and proton conductivity in some kdp-family crystals

Баранов, А. І.; Khiznichenko, V. P.; Shuvalov, L. A.

doi:10.1080/00150198908007907

Cited by 154 publications

(101 citation statements)

References 13 publications

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“…The paraelectric monoclinic phase of CDP does not change its P2 1 /m space symmetry group and from the crystallographic point of view is stable over the temperature range from the temperature of the ferroelectric phase transition (T c ϭϪ120°C) to the temperature of the superionic phase transition (T s ϭ231°C). The model for the superionic phase transition where the increase of symmetry from monoclinic to cubic is used to explain the transition from a low to a high conductivity phase 14 seems to be valid for CDP.…”

mentioning

confidence: 99%

Comment on “Does the structural superionic phase transition at 231 °C in CsH2PO4 really not exist?” [J. Chem. Phys. 110, 4847 (1999)]

Bronowska

2001

The Journal of Chemical Physics

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Superionic materials have intrigued researchers because they exhibit structural transitions from the paraelectric to the superionic phase which are accompanied by an increase of the electrical conductivity as much as five orders of magnitude. Notwithstanding the number of studies and variety of experiments that have been carried out on superprotonic crystals of the KH 2 PO 4 type, no generally agreed-upon model describing the structural and chemical features that induce superionic transitions exists. Discrepancies between the high-temperature results reported by different groups of scientists have been well summarized in recent papers. 1,2 Lee 1 has discussed the similarities of the phase transitions in the KH 2 PO 4 -type compounds and concluded that the high-temperature phenomena of these compounds are not related to physical changes like structural phase transitions, but related to chemical ones and has suggested that the term ''high-temperature phase transition'' should be replaced by ''onset of partial polymerization at reaction sites distributed on the surface of solids. '' In order to check if the reported high-temperature phase transitions of CsH 2 PO 4 ͑CDP͒ are only related to thermal dehydration, power x-ray measurements were performed by Ortiz et al.2 A fresh powder sample was subsequently heat treated 1 min at 130, 165, 200, 238, and 250°C, and their respective x-ray diffraction patterns taken under dry conditions after cooling at room temperature ͑25°C͒ were plotted ͑see Fig. 3 of Ref. 2͒. That strategy of the experiment is very good for presenting the thermal decomposition process of CDP as a function of annealing temperature; however, it is insufficient to conclude that the reported transition 3-12 associated with endothermic anomaly at ca. 231°C does not take place and, moreover, that the high conductivity above 231°C is only a consequence of the dehydration of the crystal surface.Under normal air conditions the high-temperature transition occurs very close to the region where CDP decomposes by dehydration and these two simultaneous effects considerably complicate the interpretation of the phase relation.Ten years ago the Bond method of precise lattice parameter determination was applied as a sensitive monitor of the structural changes occurring in the CDP crystal.9 Lattice parameters of CDP were calculated on the basis of the measurements of the Bragg angles of the reflections with high angles using the least-square method. The accuracy of the measurements of 2, which was better than 10Љ of arc, allowed the determination of the lattice parameters to an accuracy better than 3ϫ10Ϫ5 . Investigations of the lattice parameters of CDP above room temperature have revealed that up to ca. 137°C all parameters are almost linear. In the vicinity of 149°C a discrepancy of the linearity of the lattice parameters has been noticed, but the space group ( P2 1 /m) of the crystal above room temperature up to ca. 231°C does not change. The investigation of the single-crystal samples of CDP with the Bond diff...

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confidence: 99%

Comment on “Does the structural superionic phase transition at 231 °C in CsH2PO4 really not exist?” [J. Chem. Phys. 110, 4847 (1999)]

Bronowska

2001

The Journal of Chemical Physics

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“…The number of protons in these crystals is several times smaller than the number of possible hydrogen bonds. As a result a dynamically disordered network of hydrogen bonds is formed at higher temperatures leading to the high protonic conductivity of the order of 10 -2 Ω-1 cm -1 [3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

EPR Application in the Study of K₃H(SO₄)₂Proton Conductor Doped with Mn²⁺or VO²⁺Ions

Waplak

1994

Acta Phys. Pol. A

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The EPR of Mn 2+ -or VO 2 +-doped superprotonic conductor K3H(SO4)2 is studied in the 80-471 K temperature range. VO 2 + EPR spectrum reveals diffusion induced merging of proton transferred superhyperfine structure above 380 K. Line width anomaly is observed in Mn 2 + EPR spectrum which is attributed to the intrabond and interbond proton motions, these lead to high protonic conductivity. It is shown that paramagnetic centers namely of electronic spin greater than 1, with excess charge compensated by the protonic vacancy, are good probes to monitor the protonic conductivity on molecular level. . PACS numbers: 61.50. -f, 76.30.-v

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“…Studies have been focusing on CDP [3,4,13,14] due to its stability in hydrogen-rich surroundings. Solid acid is mixed with another solid acid and/or a hygroscopic oxide to produce a solid acid composite with higher conductivity values and improved thermal properties and stability.…”

Section: Introductionmentioning

confidence: 99%

CONDUCTIVITY AND THERMAL STABILITY OF SOLID ACID COMPOSITES CsH2PO4/NaH2PO4/SiO2

Mohammad

Mohamad²,

Kadhum³

et al. 2016

MJAS

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Solid acid composites CsH 2 PO 4 /NaH 2 PO 4 /SiO 2 with different mole ratios of CsH 2 PO 4 and NaH 2 PO 4 to SiO 2 were synthesized and characterized. Preliminary infrared measurements of CsH 2 PO 4 and its composites indicated that hydrogen bonds breaking and formation were detected between 1710 to 2710 cm -1 , while the rotation of phosphate tetrahedral anions occurred between 900 and 1200 cm -1 . The superprotonic transition of CsH 2 PO 4 /NaH 2 PO 4 /SiO 2 composite was identified at superprotonic temperatures between 230 and 260 °C, under atmospheric pressure. This study reveals higher conductivity values for composites with higher CsH 2 PO 4 (CDP) content. Solid acid composite CDP 613 appeared as the composite with the highest conductivity that is 7.2 x 10 -3 S cm -1 at 230 °C. Thermal stability of the solid acid composites such as temperature of dehydration, melting and decomposition were investigated. The addition of NaH 2 PO 4 lowers the dehydration temperature of the solid acid composites.Keywords: solid acid, conductivity, thermal analysis, caesium dihydrogen phosphate, fuel cell Abstrak Asid pepejal komposit CsH 2 PO 4 /NaH 2 PO 4 /SiO 2 dengan nisbah mol CsH 2 PO 4 kepada SiO 2 dan NaH 2 PO 4 kepada SiO 2 yang berbeza telah disintesis dan dicirikan dalam ujikaji ini. Pencirian awal sinar inframerah menunjukkan bahawa pemecahan dan pembentukan ikatan hidrogen dikesan antara 1710 cm -1 dan 2710 cm -1 , manakala putaran anion tetrahedron fosfat berlaku diantara 900 cm -1 dan 1200 cm -1 . Fasa peralihan berkonduktiviti tinggi bagi asid pepejal komposit CsH 2 PO 4 /NaH 2 PO 4 /SiO 2 telah dikenal pasti antara suhu 230 hingga 260 °C, di bawah tekanan atmosfera. Nilai kekonduksian proton adalah lebih tinggi bagi komposit yang mempunyai kandungan CsH 2 PO 4 (CDP) yang lebih tinggi. Asid pepejal komposit CDP 613 telah muncul sebagai komposit dengan kekonduksian tertinggi iaitu 7.2 x 10 -3 S cm -1 pada suhu 230 °C. Kestabilan terma asid pepejal komposit seperti suhu dehidrasi, takat lebur dan penguraian telah dikenal pasti melalui analisis termogravimetri dan kalorimeter imbasan perbezaan. Penambahan NaH 2 PO 4 merendahkan suhu dehidrasi asid pepejal komposit.Kata kunci: asid pepejal, kekonduksian, analisa terma, sesium dihidrogen fosfat, sel bahanapi Introduction Solid acids emerged as a potential solid electrolyte for fuel cell applications due to its high proton conductivity, also known as superprotonic conductivity as the conductivity values increases by 2 to 3 orders of magnitude at intermediate temperatures between 100 to 250 °C, accompanied by phase transition [1]. Solid acids are defined by the basic chemical formula M a H b (XO 4 ) c where M is a monovalent or divalent metal cation, XO 4 is a tetrahedral oxyanion, and a, b, c are integers [2]. Solid acids caesium dihydrogen phosphate, CsH 2 PO 4 (CDP) and caesium

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High temperature phase transitions and proton conductivity in some kdp-family crystals

Cited by 154 publications

References 13 publications

Comment on “Does the structural superionic phase transition at 231 °C in CsH2PO4 really not exist?” [J. Chem. Phys. 110, 4847 (1999)]

Comment on “Does the structural superionic phase transition at 231 °C in CsH2PO4 really not exist?” [J. Chem. Phys. 110, 4847 (1999)]

EPR Application in the Study of K₃H(SO₄)₂Proton Conductor Doped with Mn²⁺or VO²⁺Ions

CONDUCTIVITY AND THERMAL STABILITY OF SOLID ACID COMPOSITES CsH2PO4/NaH2PO4/SiO2

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High temperature phase transitions and proton conductivity in some kdp-family crystals

Cited by 154 publications

References 13 publications

Comment on “Does the structural superionic phase transition at 231 °C in CsH2PO4 really not exist?” [J. Chem. Phys. 110, 4847 (1999)]

Comment on “Does the structural superionic phase transition at 231 °C in CsH2PO4 really not exist?” [J. Chem. Phys. 110, 4847 (1999)]

EPR Application in the Study of K3H(SO4)2Proton Conductor Doped with Mn2+or VO2+Ions

CONDUCTIVITY AND THERMAL STABILITY OF SOLID ACID COMPOSITES CsH2PO4/NaH2PO4/SiO2

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EPR Application in the Study of K₃H(SO₄)₂Proton Conductor Doped with Mn²⁺or VO²⁺Ions