Chloride flux growth of crystalline strontium niobates and nitridation to perovskite SrNbO2N

Growth of single-crystalline SrNbO2N micron particles and assembling of particulate photoanodes

“…However, using a precursor with a Sr : Nb molar ratio higher than 1, such as Sr 5 Nb 4 O 15 or Sr 4 Nb 2 O 9 , results in the inhibition of defect absorption and a reddish-brown color in SrNbO 2 N obtained through ammonolysis. 20 A similar trend is observed in the LaNbON 2 system. 18 Excess SrO and La 2 O 3 in the precursor act as Lewis base electron donors, which lower the effective positive charge of Nb( v ), and thus enhance the stability against reduction, inhibiting the formation of low-valence Nb defects.…”

“…Preparation of SrNbO 2 N Firstly, Sr 5 Nb 4 O 15 was prepared using the molten salt method following that reported in reference. 20 NaCl and KCl were crushed in an agate mortar, followed by the addition of SrCO 3 and Nb 2 O 5 , and the mixture was ground until well mixed. The molar ratio of Sr : Nb : Na : K was 1.3 : 1 : 4 : 4, with an excess of Sr to compensate for volatilization losses.…”

“…The electron-donating property (i.e., Lewis basicity) of the oxides of strongly electropositive elements (such as Sr and La) in the precursors lowers the effective positive charge on adjacent high-valence metals, inhibiting their reduction to lower valence states. 18,20 This is also the reason why Nb 2 O 5 and TiO 2 are reduced to low-valence (oxy)nitrides after thermal ammonolysis, while Sr 2 Nb 2 O 7 and La 2 Ti 2 O 7 become SrNbO 2 N and LaTiO 2 N, respectively. Therefore, a uniform distribution of the strongly electropositive element oxide and the high-valence metals in the precursor is key to maintaining the stability of high-valence metals during thermal ammonolysis and obtaining the perovskite-type oxynitrides.…”

“…24,25 In the preparation of SrNbO 2 N and LaNbON 2 by thermal ammonolysis, the molar ratio of Sr : Nb and La : Nb in the precursor has a significant impact on the properties of the resulting products. 18,20 SrNbO 2 N derived from Sr 2 Nb 2 O 7 usually contains numerous defects, exhibiting strong defect absorption in UV-vis spectroscopy, appearing blackish-brown in color, and showing small peaks of NbO x N y in the XRD pattern. However, using a precursor with a Sr : Nb molar ratio higher than 1, such as Sr 5 Nb 4 O 15 or Sr 4 Nb 2 O 9 , results in the inhibition of defect absorption and a reddish-brown color in SrNbO 2 N obtained through ammonolysis.…”

Enhanced electron collection in a particulate LaTiO2N photoanode assembled with an inserted ZnO nanorod array for photoelectrochemical water oxidation

“…1,2 In a photoanode, the core component of a PEC cell, photogenerated electrons are collected to the conductive substrate, which is an essential process of photoelectrochemical water splitting. However, metal oxynitride semiconductor materials, including LaTiO 2 N, 3,4 SrNbO 2 N, 5 BaTaO 2 N, 6 BaNbO 2 N, 7 LaNbON 2 , 8,9 and so on, which are responsive to wide visible light, are not suitable for growth on transparent conductive substrates due to harsh preparation conditions. Therefore, it is necessary to prepare semiconductor particles independently and assemble the photoanode.…”