Закономірності зміни та прогноз деяких властивостей сполук A2TeC6 (A – Li, Na, K, Rb, Cs; C – F, Cl, Br, I)

Abstract

Based on relevant literature data on inorganic and crystal chemistry, and using the experimental results obtained in the laboratories of the Department of Inorganic Chemistry of the Uzhhorod National University over the past few decades, a series of the perovskite-related ternary halides A2TeC6 (A – Li, Na, K, Rb, Cs; C – F, Cl, Br, I) have been classified and analyzed. It was established that certain important physical properties of these compounds, such as melting point TM and band gap DE, demonstrate fairly strong dependencies (correlations) on their average nuclear charges Zave; so the above properties are expected to be reasonably well predictable for the yet non-synthesized and/or non-characterized compounds belonging to the same family of chemicals. The main findings made from the analysis of the above dependencies are as follows. (1) For iodide, bromide, chloride and fluoride compounds, the substitutions Li → Na → K → Rb → Cs steadily result in an increase of the TM and DE values along with an increase of the average nuclear charges Zave. (2) The highest and lowest melting point values are predicted for the fluoride and iodide compounds, respectively. (3) Accompanied by a decrease of the Zave value, the substitutions I → Br → Cl → F in the separately taken cesium, rubidium, potassium, sodium and lithium compounds A2TeC6, leads to a regular increase of the melting point and band gap values. (4) Based on the regularities found for the experimental data reported for the A2TeC6 ternary halides, the TM and DE values have been predicted, for the first time, for a number of A2TeC6 compounds which have not yet been investigated. The dependencies TM ~ Zave and DE ~ Zave observed for the A2TeC6 ternary halides have been found to be nearly linear and, therefore, well suitable for predicting purposes. Additionally, the TM ~ Zave and DE ~ Zave correlations and regularities found for the title compounds A2TeC6 have between compared with those found earlier for the ternary halides A3B2C9 (where A – Li, Na, K, Rb, Cs; B – P, As, Sb, Bi; C – F, Cl, Br, I) which could also be regarded as the perovskite derivatives similar to A2TeC6. The similarities and features observed for both these families of compounds have been discussed. Owing to its simplicity and straightforwardness, the approach used in this study can be recommended for routine investigations of inorganic materials belonging to the same array of chemically and structurally similar compounds. Keywords: ternary halides; melting point; band gap; crystal structures.