The Changes of Thermal, Dielectric, and Optical Properties at Insertion of Small Concentrations of Ammonium to K 3 H(SO
- PDF / 971,018 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 115 Downloads / 161 Views
CTURE OF INORGANIC COMPOUNDS
The Changes of Thermal, Dielectric, and Optical Properties at Insertion of Small Concentrations of Ammonium to K3H(SO4)2 Crystals E. V. Seleznevaa,*, I. P. Makarovaa, V. V. Grebeneva, I. A. Malyshkinab, V. A. Komornikova, N. D. Gavrilovab, R. Chitrac, and R. R. Choudhuryc a Shubnikov
Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” Russian Academy of Sciences, Moscow, 119333 Russia b Faculty of Physics, Moscow State University, Moscow, 119991 Russia c Solid State Physics Division Bhabha Atomic Research Centre, Trombay, Mumbai, 400085 India *e-mail: [email protected] Received November 28, 2017
Abstract—The structure of (K1 –x(NH4)x)3H(SO4)2 crystals with a low ammonium concentration and the behavior of their thermal, optical, and dielectric properties in a temperature range of 275–500 K have been investigated to clarify the influence of doping on the phase transition kinetics. An examination of unit-cell parameters of (K1 –x(NH4)x)3H(SO4)2 single crystals has confirmed the existence of a superprotonic phase transition at a temperature of ≈450K. The conducting properties of single-crystal and polycrystalline samples have been studied. DOI: 10.1134/S1063774518040247
INTRODUCTION The superprotonic crystals under study belong to the MmHn(AO4)(m + n)/2 · yH2O family (М = K, Rb, Cs, NH4; AO4 = SO4, SeO4, HAsO4, HPO4) [1, 2], whose specific feature is disordering of the system of hydrogen bonds at phase transitions (PTs). As a result of bond transformation, the physicochemical properties of crystals radically change at relatively low temperatures; this change gives rise to high proton conductivity, which is close in order of magnitude to the conductivity of melts of these salts (10–3–10–1 Ω–1 cm–1). This work is a continuation of the studies of (K,NH4)3H(SO4)2 crystals grown in the K3H(SO4)2– (NH4)3H(SO4)2–H2O salt system [3, 4]. This system is interesting for establishing a relationship between the kinetic features of superprotonic PTs in K3H(SO4)2 crystals [5] and their structure. Here, we performed a comparative analysis of the new results obtained for the (K,NH4)3H(SO4)2 crystals grown from solutions with a ratio of K + : NH4+ ≈ 7 : 3 with the previous data on the K3H(SO4)2 [5] and (K,NH4)3H(SO4)2 crystals grown from solutions with ratios of K + : NH4+ ≈ 9 : 1 [3, 4] and 8 : 2 [4].
EXPERIMENTAL To analyze the influence of isomorphic substitution on the PT kinetics, we investigated the crystal structure, in particular, analyzed the replacement of potassium with ammonium groups and the behavior of the thermal, optical, and dielectric properties of these crystals upon heating. The thermal properties of crystals were studied using synchronous thermal analysis, in particular, differential scanning calorimetry (DSC) and thermal gravimetric (TG) analysis. Measurements were performed on single-crystal and polycrystalline samples in a dry argon flow on a combined TG–DSC analyzer STA 449 F1 Jupiter (NETZSCH, Germany) in a temperature range of
Data Loading...
