Characterization and photocatalytic activity of Y-doped BiFeO₃ ceramics prepared by solid-state reaction method

Highlights

• Yttrium-doped bismuth iron oxide were synthesized by solid-state reaction and sintering.

• Enhanced magnetic, optical and ferroelectric properties were observed.

• The BYFO nanocomposites displayed substantial activity in degradations of methyl orange.

Abstract

Singe phase bismuth ferrite doped by yttrium (Bi_1−xY_xFeO₃, x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25) was synthesized by solid-state reaction followed by sintering. Their structural, morphological, ferroelectric, magnetic and optical properties were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), vibrating sample magnetometer (VSM) and UV–visible spectrophotometry. Rhombohedrally-distorted perovskite structure of bismuth ferrite was confirmed by XRD analysis and Rietveld refinement. Microstrain and crystallite size were analyzed using Williamson-Hall model. SEM micrographs showed agglomerated particles. The doping of yttrium into the BiFeO₃ (BFO) lattice enhanced the ferroelectric and magnetic properties and the leakage current density was reduced. The energy band gap was also decreased by increasing yttrium content, leading to an enhancement of light absorption capability. The photocatalytic activity of all samples has been evaluated by the decolorization of methyl orange (MO) under visible light irradiation. The results indicated that increasing the concentration of yttrium into the BiFeO₃ (BFO) structure improved the photodegradation up to 71%.

Introduction

Bismuth ferrite with a high Curie and Neel temperatures (T_C ∼ 1103 K & T_N ∼ 647 K) is the only well-known lead-free multiferroic material at and above room temperature (RT) [1], [2], [3], [4], [5]. Bulk BiFeO₃ has distorted rhombohedral perovskite structure (with the space group of R3c) and G-type antiferromagnetic order [6], [7], [8]. BFO is widely used in data storage, spintronics, sensors and magneto-electric devices [9], [10], [11], [12], [13], [14]. Furthermore, due to the narrow optical band-gap (∼2–2.2 eV) as well as excellent chemical stability, this material was given much renewed attention in photo-catalysts, photovoltaic facilities and for the degradation of organic pollutants and splitting water for hydrogen production [15], [16], [17], [18], [19], [20], [21], [22], [23], [24].

Beside these fascinating properties, bismuth ferrite has some restriction such as weak ferroelectricity, high leakage current density, poor ferroelectric reliability and inhomogeneous weak magnetization [25], [26], [27], [28]. These obstacles are induced by defects and secondary phases. In order to solve such problems and improve physical properties of BFO, many modification have been investigated, including optimizing preparation parameters [29], doping rare earth [Nd³⁺, Dy³⁺, Eu³⁺] or alkaline earth [Ba²⁺, Ca²⁺, Sr²⁺] metal elements instead of bismuth position [30], [31], [32], [33], [34], as well as transition metal ions [Co³⁺, Cr³⁺] substituted on the iron position [35], [36], [37]. Moreover, to shift the absorption edge of BFO to the larger wavelength for photocatalytic and photovoltaic applications, similar improvement have been reported [38], [39], [40]. We also reported in other work that Nd substitution in the BFO structure decreases the optical band-gap and improves photocatalytic activity of BFO catalyst [16], [41], [42].

Yttrium-doped BiFeO₃ has attracted interest due to the magnetic, electrical and optical properties of these compounds. The radius of yttrium ion (1.04 Å) is smaller than Bi³⁺ (1.17 Å) and substitution of bismuth ions by yttrium is expect to induce lattice distortion to enhance physical properties of bismuth ferrite [43], [44], [45]. In last decade, various method including solid-state, sol-gel, co-precipitation and hydrothermal methods have been developed in order to synthesize and study the physical properties of nano-sized Y-doped bismuth ferrite [46], [47], [48], [49], [50]. This research work focused on the structural, optical and ferroelectric and magnetic properties of BYFO particles, and the effect of yttrium on thermal properties, as well as, photocatalytic activity of BYFO particles prepared via mechanical activation was less investigated.

In this study, Bi_1−xY_xFeO₃ (x = 0, 0.05, 0.1, 0.15, 0.2 and 0.25) particles were successfully synthesized through a solid-state method. The effect of yttrium content on the morphology, structural, thermal, ferroelectric and magnetic properties have been investigated in detail. Moreover the photocatalytic activity of all samples was evaluated by decomposing MO under visible light irradiation.