Influence of atmospheric humidity on the symmetry and phase transitions of layered potassium oxyfluorides K 2 NbOF 5 · H 2 O
 作者： S. V. Melnikova,  N. M. Laptash 作者单位： 1Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences2Institute of Chemistry, Far-Eastern Branch of the Russian Academy of Sciences 刊名： Physics of the Solid State, 2013, Vol.55 (6), pp.1231-1235 来源数据库： Springer Journal DOI： 10.1134/S1063783413060243 英文摘要： Abstract(#br)Crystals of K 2 NbOF 5 · H 2 O have been grown, polarization optical investigations have been performed, and the birefringence and rotation angle of the optical indicatrix have been measured in the temperature range 100–400 K. It has been found that, depending on the degree of atmospheric humidity, the layered K 2 NbOF 5 · H 2 O crystal at room temperature can be in three states, namely, A, B , and C , which differ in symmetry and properties of the crystal. The K 2 NbOF 5 · H 2 O crystal in the A state exists at a relative humidity RH = 90–100% and undergoes a first-order improper ferroelastic phase transition P $\bar 1$ ↔ C 2/ m , which is accompanied by strong anomalies of the optical characteristics, twinning, and shear strain x 6 at temperatures T 2 ↓ = 308 K and T 2 ↑ =... 313 K. The most stable state of the K 2 NbOF 5 sdH 2 O crystal is the B state (RH = 20–90%), which retains the monoclinic symmetry C 2/ m in the temperature range 100–370 K. In a dry atmosphere (RH = 0–20%) or at T 1 ≈ 370 K, the crystal becomes anhydrous (K 2 NbOF 5 ) with the symmetry P 4/ nmm (the C state). The difference between the crystals in the states A and B is explained by the presence or absence of water molecules in interlayer spaces.

• atmospheric　大气的
• symmetry　对称
• layered　成层的
• humidity　湿度
• potassium
• phase　相位