Comparative study of the thermal behavior of Sr–Cu–O gels obtained by sol–gel and microwave-assisted sol–gel method

Abstract

In the literature data, several papers reported the synthesis by various chemical or physical methods of the SrCu 2 O 2 (SCO) having possible applications in thermoelectric or completely electronic devices such as solar cells, liquid crystal displays and touch screen. A great challenge is represented by the formation of the pure SrCu 2 O 2 (SCO), due to the high labiality of the Cu valence, depending on temperature. In the present paper, the thermal behavior of Sr-Cu-O gels obtained by sol-gel (SG) or microwave (MW)-assisted SG methods was studied in order to establish the appropriate thermal conditions for pure nanostructured SrCu 2 O 2 preparation. As reagents, copper and strontium acetylacetonate in alcoholic media were used. The starting solutions were homogenized either by stirring for 2 h at room temperature or were exposed to MW for 5 min at 300 W and a frequency of 2.45 GHz. Both solutions were left to gel at room temperature. The obtained gels were investigated by scanning electron microscopy, Fourier-transform infrared spectroscopy, as well as by thermal analysis combined with evolved gas analysis (TG/DTA-MS) measurements in air, inert and reducing atmospheres. For both type of samples, a stepwise thermal decomposition of the gels was noticed in a large temperature range. In the case of samples obtained by microwave-assisted SG method, a higher number of thermal effects were registered assigned to a higher number of molecular species formed in the sample. The residues obtained by non-isothermal treatment up to 900 °C, of both type of samples, were investigated by X-ray diffraction. The results demonstrate the influence of the MW on the SG synthesis and on the thermal properties of the resulted gels. Based on the obtained results, the required thermal treatment of the gels in order to obtain convenient precursors powders for obtaining pure SrCu 2 O 2 could be proposed.

Mechanochemical and microwave treatment of precipitated zirconium dioxide and study of its physical–chemical, thermal and photocatalytic properties

“…A similar effect but in a shorter time can be achieved using the hydrothermal treatment with microwave heating (microwave treatment, MWT) [13][14][15]. As well hydrothermal conditions are satisfied during the mechanochemical treatment (MChT) in water [16,17].…”

Influence of the Microwaves on the Sol-Gel Syntheses and on the Properties of the Resulting Oxide Nanostructures

“…Less attention was given to study the reactions that take place in the sol-gel solutions during MW irradiation [42][43][44][45].…”

“…The interest for the SrCu 2 O 2 compound are connected to its possible applications as thermoelectric or full oxide electronic devices, solar cells, liquid-crystal displays, touchscreen, and so on [45].…”

“…Predoana et al, are the first to report the synthesis of Sr-Cu-O gels by microwave (MW) assisted sol-gel methods [45]. Pure strontium acetyl acetonate (Sr(C 5 H 7 O 2 ) 2 and copper (II) acetyl acetonate (Cu(C 5 H 7 O 2 ) 2 ) were used as precursors for strontium and copper, respectively.…”

“…This result could be attributed to the formation of a higher number of molecular species with higher thermal stability. [45] (Reproduced by the permission of Elsevier).…”