Sijun Luo - Academia.edu (original) (raw)

Papers by Sijun Luo

Materials Letters, Jul 1, 2012

Transparent Pb(Zn 1/3 Nb 2/3)O 3-(Pb 1-x La x)(Zr 1-y Ti y)O 3 (PZN-PLZT) ferroelectric ceramics ... more Transparent Pb(Zn 1/3 Nb 2/3)O 3-(Pb 1-x La x)(Zr 1-y Ti y)O 3 (PZN-PLZT) ferroelectric ceramics have successfully been prepared by hot-pressed sintering in oxygen atmosphere. Uniform cylindrical samples with diameter as large as ‫ס‬ 50 mm can readily be obtained. X-ray analysis and scanning electron microscopy experiments showed a pure perovskite phase, thin grain boundaries, and uniform dense microstructures. Very good transparency was reached for wavelength from near ultraviolet to infrared. The dielectric constant was also measured as a function of temperature and frequency. Some novel phenomena such as good piezoelectric and electro-optical properties have been observed.

Ceramics International, 2017

Zr-Al-C was in-situ synthesized as a toughening component in ZrB 2-SiC ceramics by spark plasma s... more Zr-Al-C was in-situ synthesized as a toughening component in ZrB 2-SiC ceramics by spark plasma sintering (SPS) ball-milled ZrB 2-based composite powders with SiC and graphite powders. The phase composition of Zr-Al-C toughened ZrB 2-SiC (ZSA) composite ceramics fabricated through the two-step process (ball milling and SPS) did not change dramatically with varying content of Zr-Al-C which shows a major phase of Zr 3 Al 4 C 6. With increasing Zr-Al-C content, the fracture toughness of the ZSA ceramics initially increased and then decreased when the content reached 40 vol%. The ZSA ceramic with 30 vol% Zr-Al-C exhibited a maximum fracture toughness value of 5.96 ± 0.31 MPa m 1/2 , about 22% higher than that of the ZSA ceramic with 10 vol% Zr-Al-C. When the Zr-Al-C content goes beyond 30 vol%, the higher open porosity and component agglomeration led to the relatively lower fracture toughness. Crack deflection and bridging resulted from the weak interface bonding between Zr-Al-C and matrix phases and the weak internal layers of Zr-Al-C crystals, leading to longer crack paths and, hence, the toughened ZSA composite ceramics. Compared to the one-step in-situ synthesis process of Zr-Al-C and the direct incorporation process of synthesized Zr-Al-C grains, the two-step in-situ synthesis process not only led to the more uniform distribution of different components but also resulted in a much larger size of Zr-Al-C grains with a large aspect ratio causing longer crack propagation path as the result of crack deflection and bridging. The larger Zr-Al-C grains combined with the more homogeneous microstructure achieve the most substantial toughening of the ZSA composite ceramics. This work points out a promising approach to control and optimize the microstructure and improve the fracture toughness of ZrB 2-SiC composite ceramics by selecting the incorporation process of compound reinforcement components.

Applied Physics Letters

Willemite-type Zn2GeO4 is a promising ultrawide bandgap semiconductor material. To date, experime... more Willemite-type Zn2GeO4 is a promising ultrawide bandgap semiconductor material. To date, experimental results on growth and physical properties of epitaxial thin films of willemite-type Zn2GeO4 are not available. Here, we report the heteroepitaxial growth of (00.1)-oriented Zn2GeO4 thin films on c-plane sapphire substrates using pulsed laser deposition. The in-plane orientation relationships are [11.0] Zn2GeO4//[11.0] Al2O3 and [[Formula: see text]] Zn2GeO4//[[Formula: see text]] Al2O3. A 450 nm thick epitaxial film with a surface roughness of 2.5 nm deposited under 0.1 mbar oxygen partial pressure exhibits a full width at half maximum (FWHM) of rocking curve of (00.6) reflex of 0.35°. The direct bandgap is evaluated to be 4.9 ± 0.1 eV. The valence band maximum is determined to be 3.7 ± 0.1 eV below the Fermi level. Together with the density-functional theory band structure calculation, it is suggested that the O 2p orbital and Zn 3d orbital dominantly contribute to the valence band...

RSC Advances

We describe the instantaneous fabrication of a highly porous three-dimensional (3D) nanostructure... more We describe the instantaneous fabrication of a highly porous three-dimensional (3D) nanostructured manganese oxides-reduced graphitic oxide (MnOx-rGO) electrode by using a pulse-photonic processing technique.

ACS Applied Materials & Interfaces

Perovskite oxynitride semiconductors have attracted huge interest recently, as promising photoele... more Perovskite oxynitride semiconductors have attracted huge interest recently, as promising photoelectrode materials for photoelectrochemical (PEC) water splitting, depicted by, the extensive studies of the PEC activity of oxynitride powder-based photoelectrodes and/or deposited thin film electrodes. High crystalline quality, oxynitride thin films grown by physical vapor deposition are ideal

physica status solidi (RRL) – Rapid Research Letters, 2021

Heteroepitaxy of complex oxide thin films is a significant challenge when a large mismatch in the... more Heteroepitaxy of complex oxide thin films is a significant challenge when a large mismatch in the lattice parameters (> 8 %) and difference in the crystallographic symmetry coexist between the film and substrate. This work reports the heteroepitaxial growth of a hexagonal delafossite CuFeO2 thin film with (00.1) orientation on a cubic perovskite (001) SrTiO3 substrate through translational and rotational domain matching epitaxy. The rotational in-plane domain orientation relationships are CuFeO2 [11.0] // SrTiO3 [110] and CuFeO2 [2-1.0] // SrTiO3 [110] with about 10 % in-plane lattice mismatch. The 14.8 nm thick (00.1) CuFeO2 thin film shows high crystalline quality with a full width at half maximum of rocking curve of about 0.24 degrees and exhibits a possible indirect optical bandgap of 1.43 eV or direct optical bandgap of 1.94 eV. This study not only reports a model system demonstrating translational and rotational domain matching heteroepitaxy of complex oxides, but

Bulletin of the American Physical Society, 2020

Bulletin of the American Physical Society, 2017

physica status solidi (RRL) – Rapid Research Letters, 2020

Heteroepitaxial ZnGa 2 O 4 thin films grown on sapphire substrates would be preferable for fundam... more Heteroepitaxial ZnGa 2 O 4 thin films grown on sapphire substrates would be preferable for fundamental studies on properties of this material for device applications. To achieve nearstoichiometric ZnGa 2 O 4 epitaxial thin films by pulsed laser deposition (PLD), the severe loss of Zn must be overcome. This work reports the fabrication and characterization of epitaxial (111) ZnGa 2 O 4 thin films grown on (00.1) sapphire substrates by PLD using a Zn 0.97 Ga 0.03 O target. A deposition temperature of 750 ℃ and a laser fluence of 3.5 J cm-2 are suitable for growing nearstoichiometric ZnGa 2 O 4 film. The in-plane orientation relationship is identified to be [ 1 � 1 � 2] ZnGa 2 O 4 // [11.0] Al 2 O 3. A 14.2 nm thick (111) ZnGa 2 O 4 epitaxial thin film with a Zn/Ga atomic ratio of about 0.47 shows a narrow full width at half maximum value for the rocking curve of 0.1 degree and a direct optical bandgap of 4.9 eV.

Journal of Applied Physics, 2020

Thickness-dependent microstructural properties of heteroepitaxial (00.1) CuFeO2 thin films on (00... more Thickness-dependent microstructural properties of heteroepitaxial (00.1) CuFeO2 thin films on (00.1) sapphire by pulsed laser deposition

ECS Meeting Abstracts, 2017

Journal of the Ceramic Society of Japan, 2019

ZrB 2 /ZrAlC composite ceramics were successfully synthesized from Zr, Al, graphite and ZrB 2 pow... more ZrB 2 /ZrAlC composite ceramics were successfully synthesized from Zr, Al, graphite and ZrB 2 powders by using a spark plasma sintering method. The volume content of ZrAlC has a major impact on the fracture toughness. ZrAlC-rich (²70 vol.%) composite ceramics exhibit much higher fracture toughness than do ZrB 2-rich (²60 vol.%) composite ceramics. The evidently larger ZrAlC grains in the ZrAlC-rich composite ceramics lead to a longer crack propagation path for toughening. Both the Vickers hardness and Young's modulus of composite ceramics increase slightly with an increase in the ZrB 2 volume content. The evident oxidation of composite ceramics at 1000°C results in the formation of Al 18 B 4 O 33 and Al 4 B 2 O 9. At 1200°C, the composite ceramics exhibit a fluffy and porous top oxidized layer composed of whiskers of Al 18 B 4 O 33 and Al 4 B 2 O 9 grains, and the thickness of the oxidized layer and oxidation mass gain increase with an increase in the ZrAlC volume content. The ZrB 2-rich composite ceramics with less than 40 vol.% ZrAlC content do not exhibit apparently larger oxidation mass gain than does the pure ZrB 2 ceramic after oxidation at 1200°C and higher temperatures. The composition-dependent microstructure and properties provide a comprehensive insight for the development of high-temperature composite ceramics based on ZrAlC and ZrB 2 .

Journal of the Ceramic Society of Japan, 2018

ZrB 2 SiC composite ceramics were fabricated by spark plasma sintering SiC powders with various m... more ZrB 2 SiC composite ceramics were fabricated by spark plasma sintering SiC powders with various mixtures of ZrB 2 , Zr, Al and graphite components, toughening the ceramics through the in-situ synthesis of ZrAlC microstructures. Different microstructures of ZrAlC toughened ZrB 2 SiC (ZSA) composite ceramics were formed during the sintering process by varying the components ball milled with the ZrB 2 powders prior to sintering. When the milled ZrB 2-based powders contained Al, the major ZrAlC phase changed into Zr 3 Al 4 C 6 from the designed Zr 2 Al 4 C 5 , and the layered ZrAlC grains formed with a large aspect ratio in the ZSA ceramics due to the formation of an Al-based coating layer covering the ZrB 2 powders during milling process. The Zr and Al co-milled ZrB 2-based powders further improved the toughness of composite ceramics through a more uniform distribution and the larger aspect ratio of ZrAlC grains. As a result, the ZSA ceramic made using the milled powders of ZrB 2 , Zr and Al showed the highest fracture toughness of 5.96 MPa•m 1/2 , about 10% higher than that of the ceramic made using milled ZrB 2 and Zr powders. The toughening mechanisms are shown to be crack deflection and bridging caused by ZrAlC grains. This work points to a possible pathway to control the microstructure of ZrAlC grains for toughening ZrB 2 SiC composite ceramics.

Journal of Wuhan University of Technology-Mater. Sci. Ed., 2018

Polycrystalline Bi 4 Ti 3 O 12 thin films with various fractions of a-axis, c-axis and random ori... more Polycrystalline Bi 4 Ti 3 O 12 thin films with various fractions of a-axis, c-axis and random orientations have been grown on Pt(111)/Ti/SiO 2 /Si substrates by laser-ablation under different kinetic growth conditions. The relationship between the structure and ferroelectric property of the films was investigated, so as to explore the possibility of enhancing ferroelectric polarization by controlling the preferred orientation. The structural characterization indicated that the large growth rate and high oxygen background pressure were both favorable for the growth of non-c-axis oriented grains in the Bi 4 Ti 3 O 12 thin films. The films with high fractions of a-axis and random orientations, i e, f (a-sxis) = 28.3% and f (random) = 69.6%, could be obtained at the deposition temperature of 973 K, oxygen partial pressure of 15 Pa and laser fluence of 4.6 J/cm 2 , respectively. It was also noted that the variation of ferroelectric polarization was in accordance with the evolution non-c-axis orientation. A large value of remanent polarization (2Pr = 35.5 μC/cm 2) was obtained for the Bi 4 Ti 3 O 12 thin films with significant non-c-axis orientation, even higher than that of rare-earth-doped Bi 4 Ti 3 O 12 films.

Nanotechnology, 2018

This work reports a new technique for scalable and low-temperature processing of nanostructured T... more This work reports a new technique for scalable and low-temperature processing of nanostructured TiO2 thin films, allowing for practical manufacturing of TiO2-based devices such as perovskite solar cells at low-temperature or on flexible substrates. Dual layers of dense and mesoporous TiO2/graphitic oxide nanocomposite films are synthesized simultaneously using inkjet printing and pulsed photonic irradiation. Investigation of process parameters including precursor concentration (10-20 wt%) and exposure fluence (4.5-8.5 J cm-2) reveals control over crystalline quality, graphitic oxide phase, film thickness, dendrite density, and optical properties. Raman spectroscopy shows the E g peak, characteristic of anatase phase titania, increases in intensity with higher photonic irradiation fluence, suggesting increased crystallinity through higher fluence processing. Film thickness and dendrite density is shown to increase with precursor concentration in the printed ink. The dense base layer thickness was controlled between 20 and 80 nm. The refractive index of the films is determined by ellipsometry to be 1.92 ± 0.08 at 650 nm. Films exhibit an energy weighted optical transparency of 91.1%, in comparison to 91.3% of a thermally processed film, when in situ carbon materials were removed. Transmission and diffuse reflectance are used to determine optical band gaps of the films ranging from 2.98 to 3.38 eV in accordance with the photonic irradiation fluence and suggests tunability of TiO2 phase composition. The sheet resistance of the synthesized films is measured to be 14.54 ± 1.11 Ω/□ and 28.90 ± 2.24 Ω/□ for films as-processed and after carbon removal, respectively, which is comparable to high temperature processed TiO2 thin films. The studied electrical and optical properties of the light processed films show comparable results to traditionally processed TiO2 while offering the distinct advantages of scalable manufacturing, low-temperature processing, simultaneous bilayer fabrication, and in situ formation of removable carbon nanocomposites.

Journal of Physics D: Applied Physics, 2019

Lead-free 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) thin films were deposited on Pt(111)/TiO2... more Lead-free 0.5BaZr0.2Ti0.8O3-0.5Ba0.7Ca0.3TiO3 (BZT-BCT) thin films were deposited on Pt(111)/TiO2/SiO2/Si substrates by pulsed laser deposition. The optimal ferroelectric response with a high saturation polarization Ps ~110 μC/cm2, remnant polarization Pr ~ 32.5 μC/cm2 along with a coercive field of 0.18 MV/cm was observed from the P-E hysteresis loops under an applied frequency of 1 kHz. A giant recoverable energy-storage density of 93.52 J/cm3 at an applied electric field ~ 3.47 MV/cm was observed. The optimized BZT–BCT thin films exhibited a high dielectric constant with a low dielectric loss at room temperature like their bulk counterpart [high dielectric constant (Ɛ ~ 12181) and low dielectric loss (tan δ~0.01-0.03) properties. OPP-PFM images revealed switchable ferroelectric distinct polarization contrasts on the application of a ±12V dc voltage on the conductive tip at room temperature. Observed enhanced dielectric, ferroelectric and energy density properties of BZT-BCT thin films are useful for next generation electrical energy storage applications.

Materials Science and Engineering: A, 2015

Abstract ZrB 2 -20 vol% SiC-30 vol% Zr–Al–C (ZSA) composite ceramics were fabricated by using gra... more Abstract ZrB 2 -20 vol% SiC-30 vol% Zr–Al–C (ZSA) composite ceramics were fabricated by using graphite powders, SiC powders and ball milled Zr/Al/ZrB 2 composite powders through spark plasma sintering. The ball milling process resulted in forming Zr/Al coating layer covered ZrB 2 powders and introducing O into the composite powders despite of Ar protective atmosphere. The Zr/Al coating layer reacted with graphite powders to in situ form layered Zr–Al–C grains in ZSA composite ceramics during the sintering process. As increasing milling time longer than 1 h, the great increase in the introduced O included by Zr/Al/ZrB 2 composite powders leaded to an insufficiency in Al due to the formation of Al 2 O 3 , which resulted in a remarkable phase transition from Zr 2 Al 4 C 5 to Zr 3 Al 4 C 6 in the ZSA composite ceramics. The more sufficient mixing and combination of Zr, Al and ZrB 2 achieved by increasing milling time leaded to the more uniform distribution and the longer slenderness ratio of Zr–Al–C grains in the ZSA composite ceramics, which made the major contribution to the toughening of ZSA composite ceramics. The optimal milling time for Zr/Al/ZrB 2 composite powders was 4 h and the corresponding ZSA composite ceramic showed the maximum value of fracture toughness, 5.96±0.41 MPa m 1/2 , which is about 15% higher than that of the ZSA ceramic sintered using un-milled powders. The longer milling time of 6 h leaded to much more Al 2 O 3 and few layered Zr–Al–C grains in the ZSA ceramic that exhibited the minimum fracture toughness. The fracture mode is a mixture of inter- and intra-granular fractures, and the toughening mechanisms are the crack deflection and crack bridging that result from the existed Zr–Al–C grains with laminated microstructure.

Journal of Wuhan University of Technology-Mater. Sci. Ed., 2016

Al-doped ZnO (AZO) thin films were grown on c-sapphire substrates by laser ablation under differe... more Al-doped ZnO (AZO) thin films were grown on c-sapphire substrates by laser ablation under different oxygen partial pressures (P O2). The effect of P O2 on the crystal structure, preferred orientation as well as the electrical and optical properties of the films was investigated. The structure characterizations indicated that the as-grown films were single-phased with a wurtzite ZnO structure, showing a significant c-axis orientation. The films were well crystallized and exhibited better crystallinity and denser texture when deposited at higher P O2. At the optimum oxygen partial pressures of 10-15 Pa, the AZO thin films were epitaxially grown on c-sapphire substrates with the (0001) plane parallel to the substrate surface, i e, the epitaxial relationship was AZO (000 1) // Al 2 O 3 (000 1). With increasing P O2 , the value of Hall carrier mobility was increased remarkably while that of carrier concentration was decreased slightly, which led to an enhancement in electrical conductivity of the AZO thin films. All the films were highly transparent with an optical transmittance higher than 85 %.

Applied Physics A, 2017

Nanostructured metal oxide thin films with a large specific surface area are preferable for pract... more Nanostructured metal oxide thin films with a large specific surface area are preferable for practical device applications in energy conversion and storage. Herein, we report instantaneous (milliseconds) photonic synthesis of three-dimensional (3-D) nanostructured metal oxide thin films through the pulsed photoinitiated pyrolysis of organometallic precursor films made by chemical solution deposition. High wall-plug efficiency-pulsed photonic irradiation (xenon flash lamp, pulse width of 1.93 ms, fluence of 7.7 J/cm 2 and frequency of 1.2 Hz) is used for scalable photonic processing. The photothermal effect of subsequent pulses rapidly improves the crystalline quality of nanocrystalline metal oxide thin films in minutes. The following paper highlights pulsed photonic fabrication of 3-D nanostructured TiO 2 , Co 3 O 4 , and Fe 2 O 3 thin films, exemplifying a promising new method for the low-cost and high-throughput manufacturing of nanostructured metal oxide thin films for energy applications.