**Abstract**

A citrate pyrolysis technique is a unique route to prepare reactive precursor mixtures through an ignition process of concentrated aqueous solution. This procedure enables to synthesize highly homogeneous and fine powders for functional materials. The double-chain based superconductor Pr2Ba4Cu7O15�*<sup>δ</sup>* and double perovskite photocatalytic semiconductor Ba2Tb(Bi,Sb)O6 were synthesized by using the citrate pyrolysis technique. For the present sample with a reduction treatment for 72 h, a sharp superconducting transition appeared at an onset temperature *T*c,on=26 K accompanied by a zero-resistance state at *T*c,zero=22 K. The superconducting volume fraction estimated from the magnetization measurement showed an excellent value of � 58%. Both reduction treatment in a vacuum and subsequent quenching procedure are needed to realize higher superconductivity due to further oxygen defects. The polycrystalline samples for Ba2Tb(Bi1�*<sup>x</sup>*,Sb*x*)O6 (*x* ¼ 0 and 0.5) were formed in the monoclinic and cubic crystal structures. We conducted the gaseous 2-propanol (IPA) and methylene blue (MB) degradation experiments under a visible light irradiation, to evaluate photocatalytic activities of the powder samples. For the Sb50% substituted sample, the highest performance of MB degradation was observed. The effect of Sb-substitution on the photocatalytic degradation of MB is in direct contrast to that on the IPA decomposition under visible light irradiation. The enhanced photocatalytic properties in the citrate samples are attributed to their morphology, where fine particles are homogeneously distributed with a submicron order.

**Keywords:** citrate pyrolysis technique, double-chain based superconductor, pressure effect, double-perovskite oxide, photocatalytic semiconductor
