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Journal ArticleDOI

Transport and thermal properties of the solid electrolyte AgxCu2-xHgI4

01 Apr 1991-Solid State Communications (Pergamon)-Vol. 78, Iss: 2, pp 85-87

Abstract: Solid solutions AgxCu2-xHgI4 prepared by a solution method were characterised by powder X-ray diffraction, differential scanning calorimetry (DSC) and electrical conductivity. X-ray diffractograms showed tetragonal phases over the whole range expept for 1.14 ⩽ × ⩽ 1.30 where a single cubic phase was seen. DSC showed a strong compositional dependence in the order-disorder transition temperature. Temperature variation of electrical conductivity carried out for all compositions showed an increase in conductivity by two orders of magnitude at the transition temperature. The composition x=1.14 having a maximum room temperature conductivity with a minimum transition temperature has the characteristics of an eutectoid of the Ag2Hgl4-Cu2HgI4 system.
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Abstract: The nature of the superionic transition in Ag2 HgI4 and Cu2 HgI4 has been investigated using temper dependent powder neutron diffraction and impedance spectroscopy techniques. In the case of Ag2 HgI4 , the superionic transition occurs at Tc = 326(2) K and is accompanied by a 50-fold increase in the ionic conductivity. In the Cu+ analogue, which has a lower conductivity for a given temperature, the corresponding values are Tc = 338(4) K and / ~ 6. The ambient temperature crystal structures of the two compounds are different (space group I for -Ag2 HgI4 and I 2m for -Cu2 HgI4 ) but, in contrast to the most recent study, the high temperature polymorphs are found to be isostructural (space group F 3m ). Possible explanations for the different behaviour of the ionic conductivity of the two compounds are given.

24 citations

Journal ArticleDOI
A. Mary Sukeshini1, K. Hariharan1Institutions (1)
Abstract: Lattice parameters of the solid electrolyte Ag x Cu 2− x HgI 4 have been determined for the different values of x between 0 and 2. All compositions studied showed a tetragonal phase, except for a small range from x = 1.14 to x = 1.30. Compositions in this range had a cubic phase. The lattice parameters a and c of compositions outside this range increased steadily from 6.07 and 12.15A˚, respectively, for x = 0 (Cu 2 HgI 4 ) to 6.29 and 12.55A˚for x = 2 (Ag 2 HgI 4 ). Compositions in the region1.14 ≤ x ≦ 1.3 that had cubic phases were found to have lattice parameter a between 6.22 and 6.26A˚. The frequency-dependent conductivity of all compositions showed two distinct regions at low temperatures: a frequency-independent plateau region at lower frequencies (1 Hz to 10 kHz) and a power law variation,Aω n , at higher frequencies (10 to 65 kHz). At higher temperatures (>328 K) electrode polarization effects were seen at low frequencies and a frequency-independent plateau region at higher frequencies. The frequency-independent (i.e., dc) conductivity was on the order of 10 −5 (Ω cm −1 ) for compositions1.14 ≤ x ≤ 1.3.

2 citations

Journal ArticleDOI
TL;DR: All-inorganic thermochromic compounds of (Ag1-xCux)2HgI4 were synthesized by solvent-free simple and scalable mechanochemical grinding at room temperature and the phase transition temperature varied with solid solution compositions.
Abstract: Thermochromic materials are generally synthesized via high-temperature melting reaction or solution-based synthesis. Herein, all-inorganic thermochromic compounds of (Ag1-x Cux )2 HgI4 were synthesized by solvent-free simple and scalable mechanochemical grinding at room temperature. Temperature-dependent electronic absorption spectroscopy along with DSC analysis confirmed the thermochromic events within these materials, and the phase transition temperature varied with solid solution compositions. The photoluminescence (PL) spectra is red-shifted with the increase in the Cu content in (Ag1-x Cux )2 HgI4 (x=0-1).

1 citations

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K. Funke1Institutions (1)
Abstract: Most ionic crystals have degrees of disorder well below 10-2, (i). The defect concentrations being small, only a limited fraction of ions can move at a time and carry charge through the crystal lattice. The ionic conductivities of these "normal" ionic crystals are therefore low at moderate temperatures. Typical values are ca. iO -4 (~ cm) -I in the case of igCl (~) and ca. I0 -~ (9 em) -I in the case of NaCI (j), both at 200 °C. In these "normal" crystals the energy required for the formation of a defect pair greatly exceeds the thermal energy, kBT. At 200 °C the factors are ca. 95 and 50 in the cases of AgCI and NaCI, respectively (2,9). The concentrations of acfects and mobile ions in a typical ionic crystal therefore strcngiy depenu on temperature, and the same is true of the ionic conductivity.

225 citations

Journal ArticleDOI
Abstract: The structure and transformation behavior of β-Ag2HgI4 have been investigated by X-ray diffraction methods using single crystals. It has been verified that a single crystal of the β-form, stable at room temperature, transforms to a single crystal of the α-phase, stable above 50°C. The reverse transformation, α → β, on the other hand, is found to result in a multidomain arrangement of the β-phase and not to yield a new cubic modification. The β-structure is tetragonal: a = 6.322 (2) A, c = 12.605 (15) A, with space group I 4 and Z = 2. The chalcopyrite type of cation ordering, proposed by Hahn et al. (7), is confirmed. The iodine arrangement is considerably distorted from ideal cubic close packing with preservation of normal cation-iodine distances. No significant amount of disorder or occupancy of vacant sites has been found.

44 citations

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