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橙色掛燈

About us

   Welcome to the Functional Materials Laboratory at the Department of Materials Science and Engineering, National Cheng Kung University (NCKU). We are developing a range of functional materials for various applications, including magnetoelectric multiferroics, white-LED phosphors, solar photovoltaic cells, dielectric energy storage capacitors, and high-Tc superconductors. Headed by Prof. Xiaoding Qi, the research team includes two Ph.D. and nine MSc’s students.

Highlights of Recent Results

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High recoverable energy density (Wrec) and efficiency (η) in (1-x)(0.3BiFeO3-0.7SrTiO3)-xK0.5Na0.5NbO3 (BFO-STO-xKNN, x=1.0%) ceramics: https://doi.org/10.1016/j.ceramint.2022.05.240. The samples exhibit good thermal stability of Wrec and η, which vary only 4.0% and 0.8%, respectively, over the temperature range between 25-100°C, ideal for practical application.

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The BFO-STO-xKNN ceramics also show good charge/discharge performance, which is fast, in the order of 100s nanoseconds.

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Magnetoelectric voltage coefficient (αE) vs. frequency of BFO-NZFO composite films grown on the LNO nanocolumnar buffers, showing very large αE (~3.2 V/Oe•cm) can be achieved in thin-film owing to lack of substrate clamping.

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(a) low-resolution cross-sectional TEM, (b) high-resolution TEM at BFO/LNO interface, (c) high-resolution TEM at the region enclosing all three interfaces of NZFO/LNO, BFO/ LNO and NZFO/BFO, (d) magnified image of LNO layer to highlight the columnar nanostructure, inset: SAED pattern.

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The architecture of an all-oxide spin valve with the ferroelectric anti-ferromagnet BFO as the pinning layer. The multi-layered heterostructure was grown epitaxially on a (001)STO substrate and magneto-resistance was achieved at room temperature, which was switchable magnetically in a similar way to conventional metallic spin valves.

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XPS compositional depth profiling for the ZNFO/BFO interface grown at (a) 600°C, (b) 550°C, and (c) 550°C with the BFO film being annealed in 13000 Pa oxygen for 10 min prior to the deposition of ZNFO, showing a gradual reduction in Bi diffusion from BFO into ZNFO. (d–f) High-resolution TEM images of the ZNFO/BFO interface grown under the same conditions as (a), (b), and (c), respectively. (g–i) M–H hysteresis loops recorded after field annealing for the same three samples as in (d)–(f), respectively.

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(a) AFM image, image area 2 × 2 µm2, RMS roughness 2.1 nm, film thickness 300 nm.

(b) PFM image of a thinner sample (100 nm), image area 2.8 × 2.8µm2. Edge areas: virgin surface. Middle white square: scanned with −10 V dc bias. Dark stripes: scanned subsequently with +10 V dc bias.

(c) P–E hysteresis loops of epitaxial BFO films on LNO/STO

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Hydrothermal synthesis of pure BiFeO3 with the typical hysteresis loops of ideal ferroelectric.
(a) Surface SEM images of as-grown BiFeO3 thick films on Nb:STO substrates.
(b) Ferroelectric hysteresis loops measured at a frequency of 1.67 kHz and temperature of 300K.
(c) Cross-sectional SEM of as-grown BiFeO3 thick films on Nb:STO substrates.
(d) Cross-sectional SEM BiFeO3 thick film after mechanical polishing and ion milling.

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Mo-doped SnO2 thin films for gas sensor applications. SEM of the films sputtered at room temperature from metallic targets of Sn and Mo and then annealed in air at 500 °C.

The ethanol response and recovery curves of SnO2:7%Mo films under different operating temperatures.

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The sensitivity of SnO2:7%Mo films in various gases.

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(a) Thick film (2 um) of pure beta phase FeSe grown on LaAlO3 by liquid-phase processing at about 900 °C.

(b) EBSD patterns matched with the tetragonal P4/nmm. Inset: EBSD mapping, showing a twin orientation of (101) and (201).

(c) R-T plot of  pure beta-FeSe.

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Excitation spectra of the two emissions, (a) 490 nm  (b) 609 nm. Both can be excited by the same wavelength in the range of 440-480 nm.

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PL spectra of La1-xPrxTiNbO6 phosphors, showing two dominant emissions (490nm, 609nm) that can be blended to give out white light for blue LEDs (~447 nm) conversion.

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Relative intensities of the two can be tuned by Pr3+ concentration to give out the desired chromaticity. 2% Pr3+ gives out a near pure white light  (0.35, 0.32).

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