The Phase Transition of CsH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt; (CDP) at 505 K

Preisinger, A.; Mereiter, Kurt; Bronowska, W.

doi:10.4028/www.scientific.net/msf.166-169.511

Cited by 52 publications

(60 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…1, 75 nm Pt) shows broad Pt peaks 22 overlaid with monoclinic CsH 2 PO 4 peaks. 23 The presence of Pt diffraction peaks, observed even for films as thin as 7.5 nm (not shown), indicates that the deposited film is crystalline in nature, whereas the peak breadth suggests a small grain size.…”

Section: Resultsmentioning

confidence: 99%

Platinum thin film anodes for solid acid fuel cells

Haile

2011

Energy Environ. Sci.

View full text Add to dashboard Cite

Hydrogen electro-oxidation kinetics at the Pt | CsH 2 PO 4 interface have been evaluated. Thin films of nanocrystalline platinum 7.5-375 nm thick and 1-19 mm in diameter were sputtered atop polycrystalline discs of the proton-conducting electrolyte, CsH 2 PO 4 , by shadow-masking. The resulting Pt | CsH 2 PO 4 | Pt symmetric cells were studied under uniform H 2 -H 2 O-Ar atmospheres at temperatures of 225-250 C using AC impedance spectroscopy. For thick platinum films (>50 nm), electro-oxidation of hydrogen was found to be limited by diffusion of hydrogen through the film, whereas for thinner films, diffusion limitations are relaxed and interfacial effects become increasingly dominant. Extrapolation to vanishing film thickness implies an ultimate interfacial resistivity of 2.2 U cm 2 , likely reflecting a process at the Pt | H 2(g) interface. Films 7.5 nm in thickness displayed a total electrooxidation resistivity,R, of 3.1 U cm 2 , approaching that of Pt-based composite anodes for solid acid fuel cells (1-2 U cm 2 ). In contrast, the Pt utilization (R À1 /Pt loading), 19 S mg À1 , significantly exceeds that of composite electrodes, indicating that the thin film approach is a promising route for achieving high performance in combination with low platinum loadings.

show abstract

Section: Resultsmentioning

confidence: 99%

Platinum thin film anodes for solid acid fuel cells

Haile

2011

Energy Environ. Sci.

View full text Add to dashboard Cite

show abstract

“…12 The crystal structure of CDP at both temperatures turned out to be the same. No evidence was found for a structural phase transition between two monoclinic forms at 107°C as was earlier suggested.…”

mentioning

confidence: 95%

“…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][4][5][6][7][8][9][10][11][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.…”

mentioning

confidence: 99%

“…Oxygen and hydrogen atoms of the phosphate group are dynamically disordered. 12 The powder data of the superionic phase of CDP have been submitted to the ICDD ͑file no 45-618͒. On transition from the paraelectric phase to the superionic one, the volume per formula unit shows a sudden increase by ⌬Vϭ3.6 Å 3 and the crystal of CDP is subjected to serious strain.…”

mentioning

confidence: 99%

“…A Philips PW1050 powder diffractometer and a Paar TTK chamber with a heating stage were used to clarify this transition. 12 The measurements were performed in air and in a H 2 O-saturated atmosphere. Under normal atmosphere the superionic phase transition is obscured by the simultaneous chemical transformation of Powder diagrams of the superionic phase of CDP exhibit for 2Ͻ80°15 separate and well-resolved reflections which can be indexed as a cubic P-type lattice with aϭ4.961 Å at 237°C.…”

mentioning

confidence: 99%

See 2 more Smart Citations

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

View full text Add to dashboard Cite

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...

show abstract

The caesium phosphates Cs3(H1.5PO4)2(H2O)2, Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3

Weil

Stöger

2020

Monatsh Chem

View full text Add to dashboard Cite

The caesium phosphates Cs3(H1.5PO4)2(H2O)2 and Cs3(H1.5PO4)2 were obtained from aqueous solutions, and Cs4P2O7(H2O)4 and CsPO3 from solid state reactions, respectively. Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3 were fully structurally characterized for the first time on basis of single-crystal X-ray diffraction data recorded at − 173 °C. Monoclinic Cs3(H1.5PO4)2 (Z = 2, C2/m) represents a new structure type and comprises hydrogen phosphate groups involved in the formation of a strong non-symmetrical hydrogen bond (accompanied by a disordered H atom over a twofold rotation axis) and a very strong symmetric hydrogen bond (with the H atom situated on an inversion centre) with symmetry-related neighbouring anions. Triclinic Cs4P2O7(H2O)4 (Z = 2, P$$\bar{1}$$ 1 ¯ ) crystallizes also in a new structure type and is represented by a diphosphate group with a P–O–P bridging angle of 128.5°. Although H atoms of the water molecules were not modelled, O···O distances point to hydrogen bonds of medium strengths in the crystal structure. CsPO3 is monoclinic (Z = 4, P21/n) and belongs to the family of catena-polyphosphates (MPO3)n with a repetition period of 2. It is isotypic with the room-temperature modification of RbPO3. The crystal structure of Cs3(H1.5PO4)2(H2O)2 was re-evaluated on the basis of single-crystal X-ray diffraction data at − 173 °C, revealing that two adjacent hydrogen phosphate anions are connected by a very strong and non-symmetrical hydrogen bond, in contrast to the previously described symmetrical bonding situation derived from room temperature X-ray diffraction data. In the four title crystal structures, coordination numbers of the caesium cations range from 7 to 12. Graphic abstract

show abstract

The Phase Transition of CsH<sub>2</sub>PO<sub>4</sub> (CDP) at 505 K

Cited by 52 publications

References 0 publications

Platinum thin film anodes for solid acid fuel cells

Platinum thin film anodes for solid acid fuel cells

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

The caesium phosphates Cs3(H1.5PO4)2(H2O)2, Cs3(H1.5PO4)2, Cs4P2O7(H2O)4, and CsPO3

Contact Info

Product

Resources

About