Using Atomic Force Microscopy in the Study of Superprotonic Crystals
- PDF / 2,113,233 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 203 Views
ICAL SCIENCE OF MATERIALS
Using Atomic Force Microscopy in the Study of Superprotonic Crystals R. V. Gainutdinova, A. L. Tolstikhinaa,*, E. V. Seleznevaa, and I. P. Makarovaa aShubnikov
Institute of Crystallography, Federal Scientific Research Center “Crystallography and Photonics” of the Russian Academy of Sciences, Moscow, 119333 Russia *e-mail: [email protected] Received April 3, 2020; revised April 3, 2020; accepted April 3, 2020
Abstract—An investigation of new superprotonic crystals—namely, acid salts of potassium–ammonium sulfate (K1 – x(NH4)x)3H(SO4)2, x ≥ 0.57—is carried out. The surface morphology, domain structure, and conductivity of the samples are studied using atomic force microscopy. The stability and degradation of the surface of superprotonic crystals is first studied at the nanoscale. The data of piezoelectric response microscopy make it possible to establish that the crystal of (K0.43(NH4)0.57)3H(SO4)2 transits from the paraelectric phase to the ferroelectric phase when the temperature is decreased from 296 K to 282 K. DOI: 10.1134/S1063784220110092
INTRODUCTION Superprotonic crystals with a composition of MmHn (AO4)(m + n)/2 ⋅ yH2O (M = K, Rb, Cs, NH4; AO4 = SO4, SeO4, HPO4, HAsO4) are promising materials for creating various electrochemical devices. One of the most important characteristics of these crystals is high proton conductivity, which reaches 10–3– 10–1 Ω–1 cm–1 in the operating temperature range of 320–500 K. The conductivity of these materials is attributable to their structural features, but not to dopants, which makes them unique in the class of proton conductors [1]. Crystals of this crystals of this family undergo structural phase transitions, in which an increase in temperature and displacement of atoms leads to such a rearrangement of the hydrogen bond system that vacant crystallographically equivalent positions for the movement of protons are formed and the proton conductivity becomes anomalously high [2, 3]. Structural analysis is considered the main method for studying the features of phase transitions at the atomic level. However, additional information is needed to unambiguously interpret the data and find regular relationships between the structure and properties of crystalline materials. For this purpose, various dynamic research methods are employed, for example, observation of a sample in polarized light with constant heating, differential scanning calorimetry, and impedance spectroscopy. Atomic force microscopy (AFM) is a valuable source of information. Although this method was initially intended to characterize the surface of materials at the nanoscale, and now, it is possible to obtain qual-
itatively new data on the functional properties of a material in the bulk (phase transitions, structural subsurface inhomogeneities, defect structure, composition of complex heterogeneous systems, etc. [4, 5]) using improved techniques. In this regard, electrical modifications of AFM are of particular interest [6]. Thus, one of them, piezoelectric response microscopy (PRM),
Data Loading...
