Sol-gel coating of YBa2Cu3O7−x with TiO2 for enhanced anisotropic grain growth

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Abstract
This investigation focused on the effects of TiO2 additions (2.5–5 mol%) incorporated via sol-gel coating of powders on sintering behavior, microstructure development, electrical resistivity, and magnetic susceptibility of YBa2Cu3O7−x. Specimens were sintered at ≤ 960 °C for 6 h in all cases. TEM analysis indicated the sol-gel coating to be uniformly distributed around each particle and of thickness ∼ 20 to 40 nm. The addition of TiO2 was seen to reduce the sintering temperature by up to ∼ 200 °C, indicating the formation of a liquidus phase below that normally reported for YBa2Cu3O7-x. Grain growth and grain anisotropy behavior were influenced by TiO2 addition. A maximum in density, grain size, and anisotropy was achieved with 2.5 mol% addition sintered at 930 °C. TiO2 addition was shown to result in the formation of greater amounts of secondary phases such as Y2BaCuO2, and BaCuO2, particularly at higher TiO2 levels and sintering temperatures. The use of TiO2 additions also altered the magnetic susceptibility with the optimum response occurring for samples with 2.5 mol% TiO2 addition when sintered at 930 °C.