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Research Progress and Application Status of Ti
4
O
7
, the Functional Ceramic Material
WANG Yiwen, WANG Haidou, MA Guozheng, CHEN Shuying, HE Pengfei, DING Shuyu
Materials Reports
2019,33(1 ):143 -151. DOI:10.11896/cldb.201901016
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Ti
n
O
2
n
-1
are considered to be a kind of high-performance conductive ceramic material, which have broad application prospect and crucial research value due to its unique physical, chemical and electrochemical properties. In addition to its own ceramic characteristics, the oxygen defects in the crystal structure endow it with the metal-like conductive properties, which break up the limitation on further application of ceramic materials because of its poor conductivity. Ti
4
O
7
exhibits the best conductivity among Ti
n
O
2
n
-1
materials, what’s more, it also have many other remarkable properties such as outstanding photoresponse, strong acid and alkali corrosion resistance and better electrochemical stability, which has aroused great concern of material researchers and has been widely used in the field of electrochemistry, thermoelectric materials, energy storage material, photocatalytic degradation and so on. Currently, by virtue of its distinguished electron conductivity and chemical stability, Ti
4
O
7
was mainly used as battery electrodes and electrocatalytic support materials. The production process has been mature and commercialized.
The preparationprocess of Ti
4
O
7
still have many defects. Particle size, porosity, crystallinity and other factors all exert a great influence on the performance of Ti
4
O
7
. The method of revivifying titanium precursor at high temperature has been commonly applied to industry. However, the Ti
4
O
7
which was treated at high temperature would come out a series problems such as particle agglomeration, serious sintering and high specific surface area, resulting in the poor performance of Ti
4
O
7
. Therefore, researchers are trying to optimize the preparation process, and explore other synthetic methods at low temperature, but there are still some unsolved problems such as low product purity and high energy consumption. The details of the process need to be further studied. At present, three main issues consititute the majority of the research upon: Ⅰ. improving the purity of the product; Ⅱ. refining grain size and controlling particle size, Ⅲ. preparation of powder with controlled morphology.Researchers constantly introduce new technologies into the preparationprocess of Ti
4
O
7
. On the basis of the sol-gel method, the core-shell hollow pipe material with high specific surface area was successfully prepared via electrospining technology, while the sintering temperature was reduced by nearly 20%. The microwave heating method was firstly adopted to obtained Ti
4
O
7
with controlled structures by radiating only 30 minutes under microwave. In recent two years, with the deepening of research, various excellent properties of Ti
4
O
7
have been further developed and utilized. Ti
4
O
7
shows superior rapid charge and discharge properties and cycle stability in lithium-ion batteries, lithium-sulfur batteries, metal-air batteries, fuel cells. What’s more, it has been applied in energy storage materials, thermoelectricity materials, photoelectricity materials and many other new energy fields.
This paper introduces the composition, structure and physicochemical properties of Ti
4
O
7
, summarizes the main preparation methods and typical applications of Ti
4
O
7
ceramic, analyzes the advantages and disadvantages of various preparation methods and application requirements. And outlooks the future research directions and development trends in the field, which provide some references for the popularization and application of Ti
4
O
7
functional ceramic material.
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Research Progress of BaO-Ln
2
O
3
-TiO
2
System Microwave Dielectric Ceramics with High Permittivity and Low Loss
WANG Geng, FU Qiuyun, ZHANG Lu, SHI Hao, TIAN Fan
Materials Reports
2019,33(13 ):2151 -2158. DOI:10.11896/cldb.18050163
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Microwave dielectric ceramics is a kind of functional ceramics which can be used in microwave frequency circuits as dielectric materials. It is also a new type of electronic ceramic materials developed in recent decades, and mainly used in microwave devices such as antennas duple-xers, frequency stabilized oscillators, microwave capacitors, filters and resonators. These components have a wide range of applications in many fields such as 4G/5G mobile communication systems, global satellite positioning systems, satellite communication systems, wireless Internet and military radar. With the rapid development of the 5G mobile communication system industry, microwave components especially filters and resonators, acting as important devices in communication equipment, have received extensive attention from researchers all over the world. In order to make a further improvement in the performance of microwave components, decrease the size of microwave components and reduce manufactu-ring costs, the requirements for microwave dielectric materials are shown as follows: (1) high dielectric constant(
ε
r
); (2) high quality factor(
Q
f
); (3) near zero temperature coefficient of resonance frequency(TCF); (4) cheap, non-toxic and environmentally friendly raw materials.
From the perspective of dielectric constant, high dielectric constant microwave dielectric ceramics generally refer to the materials with dielectric constants above 70. The main material systems of high dielectric constant microwave dielectric ceramics usually include barium lanthanum titanium system(BaO-Ln
2
O
3
-TiO
2
), ABO
3
perovskite structure system, calcium lithium lanthanum titanium system, bismuth based system, lithium based system and lead based perovskite system. In the high dielectric constant microwave dielectric material system studied in recent years, the barium lanthanum titanium system has got the most attention. This system belongs to the perovskite-like tungsten bronze structure, and there are several types of voids in the structural unit with different shapes and sizes, which can be filled by ions with different valence states and radii. The filling of different ions would cause corresponding changes in the structure, and would influence the microwave dielectric properties at the same time. Based on the property above, many researchers have incorporated ions of different valences and radii into the Ba-Ln-Ti system, and desired to fill the ions into a certain space in the crystal structure, in order to obtain better microwave dielectric properties.
BaO-Ln
2
O
3
-TiO
2
system microwave dielectric ceramics is widely used in mobile communication for its good temperature stability, high permitti-vity and low loss. With the rapid development of 5G communication, the research on this system exhibits great theoretical significance and application value, therefore becoming one of the hottest research topics in microwave dielectric area.
This article first introduces the crystal structure and solid solubility limit of BaO-Ln
2
O
3
-TiO
2
ceramics, and then provides an overview of the progress on BaO-Ln
2
O
3
-TiO
2
system in recent years from several aspects including A-site substitution, B-site substitution, A/B-site collaborative substitution, combined modification, anti-reduction and low-temperature sintering. Current existed problems and future research priorities are also discussed in the end of the article.
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Effect of CuO Doping on Electrical Properties of YBCO Ceramics
ZHOU Hongming, WANG Boyi, LI Jian, CHENG Minghui
Materials Reports
2019,33(2 ):220 -224. DOI:10.11896/cldb.201902004
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Based on traditional solid-phase sintering method, three elements, Y
1
Ba
2
Cu
3
O
7-
x
(YBCO) ceramics as functional phase, glass powder as sintering aids and copper(Ⅱ) oxide (CuO) doping as dopant, can be made into the product—the CuO doped YBCO ceramics. Its microstructure, phase composition and electrical properties have been studied by SEM, XRD, EDS, micro ohm instrument and high temperature alternating humidity test chamber. The study has found that doping CuO can reduce the oxygen defects in the crystal structure of YBCO; as the CuO content increases from 0% to 3%, the ceramic density increases gradually while the resistivity decreases obviously; as the content of CuO is more than 3%, the ceramic density decreases gradually while the resistivity increases obviously; with the increase of CuO content, temperature coefficient of resistance (TCR) shifts from negative to positive gradually, and the TCR is becoming smaller and smaller; when the doping amount of CuO is 3%, the sample has the best comprehensive electrical properties—the resistivity is 1.55×10
-4
Ω·m and the resistance temperature coefficient is -1 470×10
-6
/℃.
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Effect of W Doping on Thermoelectric Properties of Zn
0.98
Al
0.02
O Ceramics
LI Huaiming, SUN Qiu, SONG Ying
Materials Reports
2019,33(12 ):1959 -1962. DOI:10.11896/cldb.18030250
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Zn
0.98-
x
Al
0.02
W
x
O (
x
=0, 0.005, 0.01, 0.02) precursor powders were synthesized via a sol-gel method and their ceramics were prepared for 5 h at 1 400 ℃ in N
2
atmosphere. The phase composition and microstructure of the samples were characterized by XRD and SEM. The effects of W doping on the thermoelectric properties of Zn
0.98
Al
0.02
O ceramics were investigated. The absolute value of the Seebeck coefficient of the material decreased first and then increased with the increase of the amount of W, and the conductivity showed an opposite trend. The sample with
x
=0.005 showed the highest power factor of 3.6×10
-4
W/(m·K) at 773 K, which is twice higher than Zn
0.98
Al
0.02
O. In addition, the doping of W effectively reduced the thermal conductivity. The highest
ZT
of 0.03 was obtained by
x
=0.005 sample at 773 K, which was 2.3 times higher than Zn
0.98
Al
0.02
O.
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The Influence of Micro-arc Oxidation Time on the Surface Morphology andProperties of Ceramic Coating Developed on TA15 Alloy
WANG Xian, YU Sirong, ZHAO Yan, ZHANG Peng, LIU Enyang, XIONG Wei
Materials Reports
2019,33(12 ):2009 -2013. DOI:10.11896/cldb.18040155
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Dense ceramic coatings were fabricated on TA15 by micro-arc oxidation for improving its hardness and corrosion resistance with NaAlO
2
, NaF and KOH as electrolyte. Surface morphology, chemical composition and phase composition of coatings were analyzed. Microhardness, surface roughness and corrosion resistance of coatings for different oxidation time were investigated. The results show that tiny honeycomb-like micro-nano pores could be seen on coatings. With the increase of oxidation time, the surface of coatings gradually became smooth. When the time was too long, pits, bulges and other defects were appeared. The surface roughness of the coatings firstly decreased and then increased. The coating was composed of TiO
2
, Al
2
O
3
and Al
2
Ti
3
phases. The surface microhardness of the coating always increased with the increase of oxidation time. The microhardness of the 50 min treated coating was 332.82HV, which increased by 59.2% compared to the matrix. The corrosion potential of the 40 min treated coating was +222.24 mV, which was 530 mV higher than that of the matrix. The corrosion current density of the 40 min treated coating was 1.73×10
-9
A/cm
2
, which was reduced to 3% of the matrix. The 40 min treated coating exhibited the best corrosion resistance.
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Preparation and Electrochemical Performance of Fe
3+
-Doped Activated Lignin Basic Woodceramics
JI Xiaoqin, SUN Delin, YU Xianchun, HAO Xiaofeng, CHEN Xinyi, ZHU Zhihong
Materials Reports
2019,33(20 ):3390 -3395. DOI:10.11896/cldb.18100183
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Activated woodceramics for electrode materials have been prepared from the carbonized materials of lignin extracted from black liquor with FeC
6
H
5
O
7
as catalyst at 1 200 ℃ for 2 h and with KOH as activation agent at 800 ℃ for 1.5 hours. The phase composition, specific surface area, pore structure and electrochemical properties of as-prepared woodceramics were performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N
2
adsorption-desorption (BET), constant current charge and discharge, and cyclic voltammetry respectively. The results show that when the ratio of ferric citrate to lignin is 1∶1, the activated lignin-based woodceramics have good graphitization characteristics, and its specific surface area can reach 712.59 m
2
/g, and the pore size is mainly distributed at 1.64 nm. The specific electrode capacitance of the electrode materials prepared in the inorganic system (6 mol/L KOH) can reach 115.6 F/g. After 2 500 cycles of charge and discharge, the specific capacitance retention rate reaches 75.2%, exhibiting good electrochemical performance and having the potential as an electrode material for an ideal electrochemical capacitor.
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Low Temperature Sintering and Microwave Dielectric Properties of SiO
2
-BPO
4
/LMZBS Glass Ceramics
LIU He, FU Renli, HE Qinjiang, LI Guojun, WANG He
Materials Reports
2019,33(18 ):3152 -3155. DOI:10.11896/cldb.19040034
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x
SiO
2
-(1-
x
)BPO
4
microwave dielectric ceramics had been prepared by solid-state reaction. The effects of LMZBS glass sintering aid on the phase composition, microstructure and microwave dielectric properties of ceramics was studied. The results show that the addition of LMZBS glass could lower the sintering temperature of SiO
2
-BPO
4
glass ceramics to 900 ℃, and the best dielectric properties of the ceramics(i.e.,
ε
r
=4.0,
Q
×
f
=22 600 GHz,
τ
f
=-22 ×10
-6
/℃) are obtained when the mass ratio of silicon and boron-phosphors is 70:30 and the addition of LMZBS is 4wt% at 900 ℃ for 2 h. Moreover, the presence of glass phase in the sintering process inhibited boron ions volatilization, which improved the microstructure and ensured excellent co-firing with Ag electrode. In addition, the introduction of CaTiO
3
can effectively adjust the
τ
f of 70SiO
2
-30BPO
4
ceramics. The ceramics possess optimum dielectric properties (
ε
r
=4.4,
Q
×
f
=17 800 GHz,
τ
f
=6×10
-6
/℃) when the addition of CaTiO
3
is 5wt% and sintered at 900 ℃, which is a promised candidate for LTCC application.
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High Energy Storage Density and Temperature Stability of CeO
2
Doped Bismuth Sodium Titanate-based Ceramics
WEI Fangbin, ZHANG Leiyang, WANG Ying, LI Yang, LIU Gang
Materials Reports
2019,33(16 ):2648 -2653. DOI:10.11896/cldb.19030157
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In order to prepare high performance dielectric ceramics which can be used in the field of pulse power capacitors, a compact and uniform NBT-ST based lead-free relaxor ferroelectric ceramics were prepared by the traditional solid-state reaction method. The energy storage density of NBT-ST-1Ce ceramic sample at room temperature was 1.07 J/cm
3
, and the energy storage efficiency was more than 80%. In addition, the ene-rgy storage efficiency of the ceramics showed a very good temperature stability which was around 95% in the temperature range of 25—150 ℃. Therefore, this kind of dielectric material has exhibited a very good potential in the field of pulse power capacitors applications.
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Influence of Ammonium Polyacrylic Acid and Ammonium Citrate Dispersants on Transmittance of Yttrium Aluminum Garnet Ceramics
SI Wei, DING Chao, PAN Wei
Materials Reports
2018,32(8 ):1209 -1212. DOI:10.11896/j.issn.1005-023X.2018.08.001
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Yttrium aluminum garnet (Y
3
Al
5
O
12
, YAG) transparent ceramics were prepared by vacuum sintering with the addition of sintering aids and dispersants into YAG precursor. The precursor of YAG was prepared via ultrasound-microwave-assisted alkoxide hydrolysis precipitation method. The crystal structures, morphology and optical properties of transparent YAG ceramics with the addition of different dispersant were investigated. The results showed that pure-phase transparent YAG ceramics could be obtained with the addition of all kinds of dispersants. By adding the ammonium polyacrylic acid (NH
4
PAA), no obvious boundaries were formed between crystalline grains and large pores emerged. With the addition of ammonium citrate (AC), well-dispersed crystalline grains could be formed with the average size of about 3 μm. The transmittance in the near-infrared waveband of the transparent YAG ceramic was 76% without the addition of dispersants. However, with the addition of NH
4
PAA, the transmittance of the transparent YAG ceramics was reduced to only 51%, and when adding AC it rose back to 78%. The result indicates that AC can refine the grain size of the transparent YAG ceramics and promote the removal of residual pores, thus contribute to the formation of transpa-rent YAG ceramics with higher transmittance.
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