Hydrothermal Synthesis of Ni₃TeO₆ and Cu₃TeO₆ Nanostructures for Magnetic and Photoconductivity Applications

Abstract

Despite great attention toward transition metal tellurates especially M3TeO6 (M = transition metal) in magnetoelectric applications, control on single phasic morphology-oriented growth of these tellurates at the nanoscale is still missing. Herein, a hydrothermal synthesis is performed to synthesize single-phased nanocrystals of two metal tellurates, i.e., Ni3TeO6 (NTO with average particle size ∼37 nm) and Cu3TeO6 (CTO ∼ 140 nm), using NaOH as an additive. This method favors the synthesis of pure NTO and CTO nanoparticles without the incorporation of Na at pH = 7 in MTO crystal structures such as Na2M2TeO6, as it happens in conventional synthesis approaches such as solid-state reaction and/or coprecipitation. Systematic characterization techniques utilizing in-house and synchrotron-based characterization methods for the morphological, structural, electronic, magnetic, and photoconductivity properties of nanomaterials showed the absence of Na in individual particulate single-phase MTO nanocrystals. Prepared MTO nanocrystals also exhibit slightly higher antiferromagnetic interactions (e.g., T N-NTO = 57 K and T N-CTO = 68 K) compared to previously reported MTO single crystals. Interestingly, NTO and CTO show not only a semiconducting nature but also photoconductivity. The proposed design scheme opens the door to any metal tellurates for controllable synthesis toward different applications. Moreover, the photoconductivity results of MTO nanomaterials prepared serve as a preliminary proof of concept for potential application as photodetectors.

Shape-Controlled Synthesis of Cu3TeO6 Nanoparticles with Photocatalytic Features

“…The EDS mappings (Figure ) of the samples show only the presence of Cu (green), Te (blue), and O (red) elements homogeneously distributed in the sample, regardless of the morphology obtained. The relative amount obtained by EDS of the elements Cu and Te is lower (Table S1) with respect to O compared with the stoichiometric ratio (Cu 3 TeO 6 ) and our previously reported results . This fact might indicate the presence of both phases (Cu 3 TeO 6 and Cu 3 TeO 6 ·H 2 O) in the samples synthesized in this work as it was observed by XRD analysis, since the Cu 3 TeO 6 ·H 2 O material has a higher stoichiometrical amount of O in its elemental structure.…”

“…The DRUV–vis spectra of the samples prepared at different pH values are shown in Figure b. All CTO samples showed two absorption ranges and an abrupt cutoff in the range of 200–500 nm as common in semiconductors. , The band gaps ( E g ) determined by Tauc plot analysis (Figure S5) demonstrate that the sample synthesized at acidic pH (CTO_4) had a lower band gap (2.46 eV) than the samples prepared at higher pH (CTO_6:2.6 eV, CTO_8:2.59 eV, and CTO_10:2.53 eV). The DRUV–vis results indicated that CTO is a semiconductor with a band gap in the range of the visible (2.6 eV), which is a very intriguing property for its use as a photocatalyst in visible light-mediated processes. ,, …”

“…One fascinating compound within the MTO family is Cu 3 TeO 6 (CTO). , The CTO crystal structure was first determined by Hostachy and Coing-boyat and was revised in 1978 . This material has a cubic structure (Ia3), which is built up by TeO 6 units connected through copper atoms .…”

“…The design and crystal growth of semiconductor materials have been drawing attention of the scientific community due to the materials’ applications in photocatalysis, photosensors, and solar cells, among others. − A promising family of semiconductor materials is metal tellurates M 3 TeO 6 (MTOs), which are composed of 3d transition metals (M) such as copper (Cu), nickel (Ni), cobalt (Co), tellurium (Te), and oxygen (O). , Until now magnetoelectric applications have been the main focus for the use of MTOs, due to their multiferroic properties. , Although, in the last years the scientific community has started to explore the application of these materials in the fields of photocatalysis, electrochemistry, and sensors, among others …”

“…In this sense, Mutharani et al showed a facile wet chemical method to prepare CTOs for their application in an electrochemical sensor . In some cases, these routes use different additives to achieve the desired composition. , However, the use of additives such as NaOH to start the precipitation and to control the morphology of the final materials can generate different phases in the target product, e.g., Na 2 Cu 2 TeO 6 . , In a recent study, our research group proposed the use of hydrothermal methodology to perform the synthesis of MTOs, Ni 3 TeO 6 and Cu 3 TeO 6 , using NaOH as an additive. We obtained single-phase crystals using the hydrothermal method at pH = 7.…”