Environmentally Benign Synthesis and Color Tuning of Strontium–Tantalum Perovskite Oxynitride and Its Solid Solutions

Abstract

A facile method was successfully developed to prepare strontium-tantalum perovskite oxynitride, SrTaO 2 N, and its solid solutions. Urea was employed as a solid nitriding agent to eliminate the use of toxic NH 3 gas. In addition, utilization of sol-gel derived Ta 2 O 5 gel as a Ta precursor allowed for completion of nitridation within a shorter period and at a lower calcination temperature compared with the conventional ammonolysis process. Optimization of the reaction conditions, such as the urea content, allowed for production of solid solutions of SrTaO 2 N and Sr 1.4 Ta 0.6 O 2.9 . The products exhibited optical absorption and chromatic colors because of the narrower band gaps of oxynitrides compared with those of oxides. The O/N ratios of the solid solutions were easily adjusted by varying the amount of urea in the mixture of precursor. As a result, the colors of the products ranged from yellow to brown. The nitridation process and products developed in this study are interesting environmentally-benign alternatives to conventional inorganic pigments.

Control of the Photocatalytic Activity of Metastable Layered Oxynitride K2LaTa2O6N through Topochemical Transformation of Tuned Oxide Precursors

“…Oxynitrides that comprise d 0 transition-metal cations (e.g., Ti 4+ , Nb 5+ , or Ta 5+ ) or d 10 typical metal cations (e.g., Ga 3+ or Ge 4+ ) exhibit semiconducting properties and hence function as photocatalysts. − Of particular importance is the presence of N-2p states in oxynitrides, which can generate narrow band gaps capable of absorbing visible light . In this context, d 0 transition-metal oxynitrides have also attracted attention as stable, nontoxic pigments. ,, …”

Non-ammonolysis synthesis and characterisation of environmentally benign yellow pigments based on calcium–tantalum perovskite oxynitrides

“…In the previous report on the preparation of SrTaO 2 N from a Ta 2 O 5 gel and urea, a single-phase synthesis was achieved by using SrCO 3 as the Sr source. 41 In this study, we thus first examined the use of CaCO 3 as the Ca source in the preparation of CaTa(O,N) 3 . Information obtained by characterisation of products synthesised with various molar ratios of urea can be used to identify the optimum conditions for the formation of perovskite oxynitrides.…”

“…In the previous report on the preparation of SrTaO 2 N from a Ta 2 O 5 gel and urea, a single-phase synthesis was achieved by using SrCO 3 as the Sr source. 41 In this study, we thus first…”

“…This is presumably because of reduction of Ta 5+ in CaTa(O,N) 3 to Ta 4+ by urea, which also acts as a reducing agent. 40,41 In other words, the dull colour arose from a tantalum species, which was reduced during the urea-nitriding process. The Commission Internationale de l'Eclairage (CIE) L*a*b*Ch1 colour coordinate parameters of CaTa(O,N) 3 prepared using CaCO 3 (Ca : Ta : urea = 2 : 1 : 5) and Ca(OH) 2 (Ca : Ta : urea = 1.5 : 1 : 3) are summarised in Table 1.…”

“…More recently, the strontium-tantalum oxynitride, SrTaO 2 N, and its solid solutions with Sr 1.4 Ta 0.6 O 2.9 have also been prepared by the urea-nitriding method using SrCO 3 and Ta 2 O 5 gel as precursors. 41 The oxygen and nitrogen contents in the solid solutions can be controlled by changing the quantity of urea in the precursor mixture. The solid solutions exhibited various chromatic colours, suggesting their potential applications as secure inorganic pigments.…”