Protonic conductivity and ferroelastic instability in triammonium hydrogen disulphate: a dielectric and neutron diffraction study
TL;DR: In this article, a phenomenological two-orderparameter model for the - ferroelastic phase transition was proposed, where properties which originate from the disorder of the oxygen and proton subsystem can be described by irreducible representations of the wave vector at the point and the L point of the Brillouin zone of the paraphase.
Abstract: The protonic conductivity of has been measured using the complex-admittance method in the frequency range 30 Hz-200 MHz and the temperature interval 290-500 K covering both the ferroelastic and the paraelastic phases. The dc conductivity shows quasi-two-dimensional behaviour and in the trigonal paraelastic phase its values in the (001) plane are typically super-protonic with low activation enthalpy . The temperature dependence of the monoclinic superstructure reflection 120 has been studied using elastic neutron diffraction. It was found that the observed anomalies of the macroscopic and microscopic quantities, such as the morphic birefringence and the high-frequency dielectric constant on the one hand and the diffusion proton dynamics as well as the integrated intensity of the reflection 120 on the other hand, show pronounced differences in their temperature evolution below the ferroelastic phase transition temperature. The neutron scattering results as well as the dielectric measurements indicate precursor effects above . The results are discussed on the basis of a phenomenological two-order-parameter model for the - ferroelastic phase transition. It is argued that properties which originate from the disorder of the oxygen and proton subsystem can be described by irreducible representations of the wave vector at the point and the L point of the Brillouin zone, while properties which originate from displacements of the heavy atoms (the displacement mode) are solely described by the wave vector at the L point of the Brillouin zone of the paraphase.
Citations
More filters
TL;DR: In this paper, the structural transitions between the phases with ordered and disordered hydrogen-bond networks are described with the emphasis being made on the structural mechanisms of anomalously high (superprotonic) conductivity associated with delocalization of hydrogen bonds.
Abstract: The class of hydrogen-containing salts in which the phases with dynamically disordered hydrogen-bond nets are formed has been considered. Unlike other hydrogen-bonded crystals, the crystals of this class are characterized by delocalized hydrogen bonds producing considerable influence on their physical and physical-chemical properties. The structural transitions between the phases with ordered and disordered hydrogen-bond networks are described with the emphasis being made on the structural mechanisms of anomalously high (superprotonic) conductivity associated with delocalization of hydrogen bonds. The perspectives of the use of crystals with delocalized hydrogen bonds in fuel cells and other electrochemical devices are discussed.
106 citations
TL;DR: The structure of letovicite, (NH4)3H(SO4)2 has been determined at 293 and 420 K as mentioned in this paper, and the structure is composed of two symmetrically independent isolated isolated NH4+ tetrahedra and [SO4−H-SO4]3− dimers with a symmetrical hydrogen bond connecting the two sulfate tetrashedra.
22 citations
TL;DR: The tris(2,6-diaminopyridinium) hydrogen sulfate sulfate monohydrate (C 5 H 8 N 3 ) 3 (HSO 4 )(SO 4 )·H 2 O, was grown by slow evaporation technique in aqueous solution.
20 citations
TL;DR: In this paper, the 1H magic-angle-spinning (MAS) NMR spectra were traced at room temperature (RT) and at Larmor frequency of 400.13MHz in the range of 135-490 K.
19 citations
TL;DR: In this paper, the phenomenon of proton conductivity in hydrogen-bonded acidic sulphate and selenate salts of alkali metals is discussed, and the superionic proton conducting state in the crystals is achieved as a result of structural phase transition at TS.
19 citations
References
More filters
TL;DR: In this paper, the proton migration mechanism via successive proton intrabond jumps and reorientation of the OH groups was studied in the low and high conductive phases of CsHSO4, CsDSO4 and Rb3H(SeO4)2 single crystals.
111 citations
89 citations
TL;DR: In this paper, a phase diagram containing three different phases a (paraelastic), b (birefringence) and c (both ferroelastic) is presented.
Abstract: Mixed crystals Pb3(PO4)2--Pb3(AsO4)2 are ferroelastic at low temperatures. The phase diagram contains three different phases a (paraelastic), \tt b and \tt c (both ferroelastic). The transformation \tt a-\tt b is first order for Pb3(PO4)2 and approaches second-order behaviour with increasing As content. The spontaneous strains and the birefringence follow approximately a Curie-Weiss law, with a corresponding order-parameter exponent β = ¼. The mutual high-temperature phases give diffuse X-ray reflections due to inelastic scattering. The soft-mode model is discussed for these results.
74 citations
TL;DR: The ferroelastic phase transitions in this article are accompanied by large excess specific heat in a wide temperature range above and below the critical crossover point, which is interpreted in terms of a multicomponent order-parameter theory.
Abstract: The ferroelastic phase transitions in ${\mathrm{Pb}}_{3}$${(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ and ${\mathrm{Pb}}_{3}{({\mathrm{P}}_{1\ensuremath{-}x}{\mathrm{As}}_{x}{\mathrm{O}}_{4})}_{2}$ are accompanied by large excess specific heats in a wide temperature range above ${T}_{c}$ and critical crossover above and below ${T}_{c}$. Critical exponents of the specific heat ${\ensuremath{\alpha}}^{\ensuremath{'}}=0.363(4), 0.360(5), \mathrm{and} 0.36(1)$ for ${\mathrm{Pb}}_{3}$(${\mathrm{P}{\mathrm{O}}_{4})}_{2}$, ${\mathrm{Pb}}_{3}$${({\mathrm{P}}_{0.97}{\mathrm{As}}_{0.03}{\mathrm{O}}_{4})}_{2}$, and ${\mathrm{Pb}}_{3}$${{(\mathrm{P}}_{0.2}{\mathrm{As}}_{0.8}{\mathrm{O}}_{4})}_{2}$, respectively, agree with theoretical predictions of a $q=3$, $d=2$, Potts model. Along with other experimental results of neutron and Raman scattering, the specific-heat behavior above ${T}_{c}$ indicates dynamical fluctuations in ${\mathrm{Pb}}_{3}$${(\mathrm{P}{\mathrm{O}}_{4})}_{2}$ and a static intermediate phase in the mixed crystals. A strict proportionality between the transition entropy $\ensuremath{\Delta}S$ and the spontaneous birefringence $\ensuremath{\Delta}{n}_{\mathrm{bc}}$ was observed in ${\mathrm{Pb}}_{3}$(${\mathrm{P}{\mathrm{O}}_{4})}_{2}$ at temperatures up to 415 K. Nonlinear behavior was found close to the transition point (453.6 K), which is interpreted in terms of a multicomponent order-parameter theory.
65 citations
TL;DR: In this article, it is shown that the symmetry of the order parameter transforms according to a three-dimensional irreducible representation of R3m corresponding to the L point of the Brillouin zone boundary of the rhombohedral lattice.
Abstract: On examine d'un point de vue theorique la transition de phase ferroelastique du phosphate de plomb Pb3(P04)2 situee a 180 °C. On remarque que le changement de symetrie spatiale R3m B2/b qui se produit a la transition, s'accompagne d'un doublement du nombre d'atomes dans la maille elementaire. Le phosphate de plomb est ainsi un materiau ferroelastique de type impropre. La symetrie du parametre d'ordre de la transition est etudiee par des methodes classiques de theorie des groupes. On montre que le parametre d'ordre se transforme suivant une representation irreductible tridimensionnelle de R3m correspondant au point L de la frontiere de la premiere zone de Brillouin du reseau rhombo-edrique. Toutefois deux representations irreductibles distinctes sont susceptibles d'induire la transition observee, laissant done subsister une ambiguite sur la symetrie reelle du parametre d'ordre. L'energie libre qui decrit revolution des proprietes physiques macro-scopiques au voisinage de la transition prend la meme forme dans les deux cas.
The 180 °C ferroelastic phase transition of lead phosphate Pb3(P04)2 is theoretically investigated. It is shown that the change in space symmetry R3m B2/b which occurs at the transition, involves a doubling in the number of atoms in the unit cell. Thus, lead phosphate is a ferroelastic material of the improper type. The symmetry of its order parameter is analysed by standard group theoretical methods. It is shown that the order parameter transforms according to a three-dimensional irreducible representation of R3m corresponding to the L point of the Brillouin zone boundary of the rhombohedral lattice. However, two distinct irreducible representations can induce the observed transition leaving an ambiguity on the actual symmetry of the order parameter. The free-energy expansion which describes the evolution of physical properties in the vicinity of the transition has the same form in both oases.
47 citations