Terahertz time domain spectroscopy of amorphous and crystalline aluminum oxide nanostructures synthesized by thermal decomposition of AACH

The objective of this work is to study the changes in optical and dielectric properties with the transformation of aluminum ammonium carbonate hydroxide (AACH) to α-alumina, using terahertz time domain spectroscopy (THz-TDS). The nanostructured AACH was synthesized by hydrothermal treatment of the r...

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Bibliographic Details
Published in:Materials chemistry and physics 2017-04, Vol.191, p.62-69
Main Authors: Mehboob, Shoaib, Mehmood, Mazhar, Ahmed, Mushtaq, Ahmad, Jamil, Tanvir, Muhammad Tauseef, Ahmad, Izhar, Hassan, Syed Mujtaba ul
Format: Article
Language:English
Subjects:
AACH
Absorptivity
Alumina
Aluminum
Aluminum oxide
Complex permittivity
Crystal structure
Dielectric properties
Fourier transforms
Hydrothermal treatment
Optical properties
Refractive index
Refractivity
Roasting
Studies
Synthesis
Temperature
Terahertz
Thermal decomposition
Time domain analysis
X-ray diffraction
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Summary:The objective of this work is to study the changes in optical and dielectric properties with the transformation of aluminum ammonium carbonate hydroxide (AACH) to α-alumina, using terahertz time domain spectroscopy (THz-TDS). The nanostructured AACH was synthesized by hydrothermal treatment of the raw chemicals at 140 °C for 12 h. This AACH was then calcined at different temperatures. The AACH was decomposed to amorphous phase at 400 °C and transformed to δ* + α-alumina at 1000 °C. Finally, the crystalline α-alumina was achieved at 1200 °C. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to identify the phases formed after calcination. The morphology of samples was studied using scanning electron microscopy (SEM), which revealed that the AACH sample had rod-like morphology which was retained in the calcined samples. THz-TDS measurements showed that AACH had lowest refractive index in the frequency range of measurements. The refractive index at 0.1 THZ increased from 2.41 for AACH to 2.58 for the amorphous phase and to 2.87 for the crystalline α-alumina. The real part of complex permittivity increased with the calcination temperature. Further, the absorption coefficient was highest for AACH, which reduced with calcination temperature. The amorphous phase had higher absorption coefficient than the crystalline alumina. •Aluminum oxide nanostructures were obtained by thermal decomposition of AACH.•Crystalline phases of aluminum oxide have higher refractive index than that of amorphous phase.•The removal of heavier ionic species led to the lower absorption of THz radiations.
ISSN:0254-0584
1879-3312
DOI:10.1016/j.matchemphys.2017.01.030