Investigation of structural, morphological, thermal, and thermoelectric properties of Zn_1−xCu_xAl₂O₄ (0.0 ≤ x ≤ 0.1)

Abstract

Most promising oxide thermoelectric materials such as perovskites, layered oxide materials, Al-doped ZnO, etc., have been reported. In the present work, Zn1-xCuxAl2O4 (0.0≤ x ≤0.1) samples were synthesized by a simple hydrothermal method. The structural, optical, morphological, and TE properties of Zn1-xCuxAl2O4 (0.0≤ x ≤0.1) have been investigated. XRD analysis reveals that ZnAl2O4 has a single-phase cubic structure and Cu is completely dissolved in the ZnAl2O4 lattice. Thermal analysis shows that ZnAl2O4 has high thermal stability up to 1000 °C. From the UV-Vis DRS analysis, the energy band gap of ZnAl2O4 decreased from 3.30 eV to 2.82 eV with increasing the content of Cu. Carrier concentration and mobility of the samples were measured by the Hall effect. The values of a carrier concentration of undoped ZnAl2O4 and Zn0.9Cu0.1Al2O4 are obtained to be 3.836×1013 cm-3 and 3.3×1016 cm-3 at 313 K and 9.6×1013 cm-3 for pure and 5.5×1016 cm-3 for Zn0.9Cu0.1Al2O4 at 673 K. TE properties of the synthesized samples have been analyzed as a function of temperature. With the optimum values of Seebeck coefficient and electrical conductivity, Zn0.9Cu0.1Al2O4 shows the highest power factor of 0.50 μW/mK2 while the pure ZnAl2O4 shows a maximum power factor of 0.19 μW/mK2 at 673 K. The Zn0.9Cu0.1Al2O4 exhibits a relatively high zT of 2.4×10-4 at 673 K, while pure ZnAl2O4 has a zT value of 0.4×10-4 at 673 K. The obtained values reveal the improvement of TE properties by increasing the Cu content in the sample.

The Effect of Different Polyol Precursors on Disordered Spinel ZnAl2O4 Structure Prepared by the Polymeric Citrate Complex Method and the Corresponding Catalytic Behavior in the Glycerolysis of Urea

“…The presence of ZnO 6 and AlO 4 sites in the gl-ZnAl 2 O 4 and s-ZnAl 2 O 4 catalysts provides evidence for the partially inverse spinel structure of ZnAl 2 O 4 . The inversion parameter, calculated as AlO 4 /(AlO 4 þ AlO 6 ) from the XPS and 27 Al-NMR measurements, along with the order parameter from the XRD data and the intensities of AlO 4 shoulder peaks from FTIR, confirmed the degree of disorder in the ZnAl 2 O 4 spinel structure. The consistent trend observed in the inversion parameter, the order parameter, and the AlO 4 shoulder peak intensities demonstrated a significant formation of the partially inverse spinel structure in the gl-ZnAl 2 O 4 and s-ZnAl 2 O 4 catalysts.…”

“…To investigate the presence of AlO 4 in the bulk ZnAl 2 O 4 , 27 Al nuclear magnetic resonance (NMR) measurements were performed. Figure S3, Supporting Information, shows that the NMR spectra exhibited four deconvoluted peaks in different chemical shift regions.…”

“…The next prominent peak at 420 cm À1 corresponds to the E g mode of vibration. [18,27] The principal Raman mode for the ZnAl 2 O 4 crystal structure is the high-frequency F 2g mode. In this material, the high-frequency mode at 660 cm À1 arises from the movement of oxygen atoms within the AlO 6 octahedral structure.…”

“…In this material, the high-frequency mode at 660 cm À1 arises from the movement of oxygen atoms within the AlO 6 octahedral structure. [18,27,28] Any disordered material defects are usually discerned by observing some asymmetry in the peak positions. [28,29] A strong peak at 720 cm À1 is identified as A* 1g .…”

“…Desorbed species were eliminated from the system using helium flow at a rate of 30 mL min À1 , and subsequently analyzed using the TCD detector. 27 Al magic angle spinning (MAS) NMR (Bruker Avance III 300, Germany) spectra were recorded using a 2.5 mm MAS probe at RT in a 7.04 T magnet. All spectra were acquired at 30 kHz (ν r ) with a rotor-synchronized Hahn-echo pulse sequence (90°-τ-180°-τ-acq), where τ = 1/ν r .…”