Photoelectrochemical properties of titanates with the hollandite structure

The photoelectrochemical properties and the diffuse reflection spectra of the titanates K_1.8M²⁺_0.9Ti_7.1O₁₆ (M²⁺ = Mg²⁺, Ni²⁺) and K_1.8M³⁺_1.8Ti_6.2O₁₆ (M³⁺ = Al³⁺, Cr³⁺) with the hollandite structure are reported. The white titanates K_1.8Mg_0.9Ti_7.1O₁₆ and K_1.8Al_1.8Ti_6.2O₁₆ show an optical absorption edge near 3.7 eV. These compositions can be coloured by transition-metal ions due to the occurrence of Meⁿ⁺ → Ti⁴⁺ charge-transfer transitions. When these coloured titanates were used as photo-anodes in a photoelectrochemical cell for water electrolysis, no photoresponse was observed with visible light irradiation. Possible reasons are discussed.     

Preparation and dielectric properties of microwave ceramics based on doped zinc titanates

We have studied the dielectric properties of microwave ceramic materials in the binary system Zn₂TiO₄-TiO₂ and examined the effect of doping with Sn²⁺, Sb³⁺, Bi³⁺, and Mg²⁺ on the dielectric properties and microstructure of the ceramics. The doped Zn-Ti-O ceramics are thermally stable and have ? = 18–33 and tan δ from 0.0001 to 0.007. Our results demonstrate that the doped Zn-Ti-O ceramics are potentially attractive for microwave applications, in particular for use as ceramic components (resonator substrates) of miniature antennas.     

Effect of barium on the structure and dielectric properties of multicomponent ceramics based on ferroelectric relaxors

High-density ceramic samples of mPb(Mg_1/3Nb_2/3) · yPb(Zn_1/3Nb_2/3) · nPb(Ni_1/3Nb_2/3) · xPbTiO₃ (m = 0.4541, y = 0.0982, n = 0.1477, x = 0.3) solid solutions, unmodified and barium-modified, with the composition lying in a morphotropic phase region, have been prepared by a conventional ceramic processing technique. We demonstrate that barium substitution for 5% of the lead on the A site allows one to obtain ceramics containing no pyrochlore phase. Modification with barium shifts the solid solution from the morphotropic to a tetragonal phase region. In addition, barium doping increases the average grain size of the ceramic from 2–3 to 3–4 μm and changes the type of fracture from intergranular to mixed (intergranular and transgranular). Modification with barium increases the relative dielectric permittivity ?/?₀ (at E = 0) of the material by more than a factor of 2 (from 4300 to 9100). We conclude that materials based on the ceramics studied can find practical application and examine ways of further improving their piezoelectric performance.     

Influence of compaction conditions on the structure and mechanical properties of potassium hexatitanate based ceramics

The influence of compacting pressure on the structure and mechanical properties of sintered ceramics based on weakly crystalline potassium polytitanate with a composition close to K₂O · 6TiO₂ has been studied. It is established that an increase in the pressure during the uniaxial cold pressing of compacts leads to the formation of a ceramic structure that consists of layers formed by compacted nanofibers of crystalline potassium hexatitanate. Relationship between the structure and mechanical properties of obtained ceramics is analyzed.     

石墨烯改性PDC-SiCNO陶瓷的制备及其介电性能

以聚乙烯基硅氮烷(PVSZ)为原料,氧化石墨烯(GO)为碳源,无水乙醇(ETOH)为分散剂,制备石墨烯球增强SiCNO陶瓷(SiCNO-GO)。利用拉曼光谱(Raman)、电子自旋共振(EPR)和扫描电子显微镜(SEM)等表征手段,研究SiCNO-GO陶瓷结构对其介电性能的影响。结果表明:SiCNO-GO陶瓷的微球密度和粒径的大小与GO的含量有关;随着SiCNO-GO陶瓷中GO含量的增加,SiCNO-GO陶瓷的介电常数和介电损耗也随之增大,在GO含量为0.1%(质量分数)时达到最大值,而当GO质量分数为0.3%时,SiCNO-GO陶瓷的介电常数和介电损耗降低。     

Preparation and dielectric properties of celsian ceramics based on hexagonal BaAl2Si2O8

Celsian ceramics based on hexagonal BaAl₂Si₂O₈ have been prepared through synthesis at 1450°C followed by firing at 1500°C. The unit-cell parameters of BaAl₂Si₂O₈ and principal bond distances in its structure have been determined by the Rietveld method. Using differential thermal analysis and temperature-dependent dielectric measurements, we have determined the temperature of the α (hexagonal) to β (hexagonal) phase transition in our samples: 280–320°C.     

Preparation and dielectric properties of potassium sodium niobate-based solid solutions

We have prepared ceramic samples of solid solutions based on Bi-containing perovskite-like oxides near the morphotropic phase boundary in the K_0.5Na_0.5NbO₃-BiScO₃-AgSbO₃ system and modified with LiF and MnO₂ additions; investigated the phase relations, structure, and dielectric and ferroelectric properties of the ceramics; and determined their phase transition temperatures. The choice of superstoichiometric additives capable of intensifying the sintering process has been substantiated, and the effect of the additives on the Curie temperature of the ceramics has been examined.     

Lead-free ceramics based on alkaline niobate tantalate antimonate with excellent dielectric and piezoelectric properties

This paper reports lead-free (Na_0.52K_0.48−x)(Nb_0.94−xSb_0.06)O₃-xLiTaO₃ compositions with significantly enhanced piezoelectric properties. The 6% Sb substituted Na_0.52K_0.48NbO₃ was modified by a small amount of LiTaO₃, leading to the formation of a morphotropic phase boundary between orthorhombic and tetragonal phases in the range of x = 0.035-0.04 where the materials show a strong compositional dependence of various electrical properties. Excellent properties of d₃₃ = 335 pC/N, k_p = 53%, , Q_m = 41 and T_c = 291 °C were obtained in the composition with x = 0.04, indicating that the ceramics studied are promising as a lead-free piezoelectric candidate.     

Preparation and microwave dielectric properties of Bi2Ti4O11 ceramics

Single phase of Bi₂Ti₄O₁₁ ceramics, which belong to meta-stable phase compounds, were synthesized by controlling the reaction time through conventional solid-state method. The effects of annealing time on phase composition of Bi₂Ti₄O₁₁ ceramic powders and sintered ceramics were studied by XRD analysis. Second phase Bi₂Ti₂O₇ appeared when the annealing time shorter than 4 h. However, pure phase of Bi₂Ti₄O₁₁ powders can be formed by prolonging the annealing time to 6 h at 1,000 °C. The sintering temperatures on microstructure and microwave dielectric properties of Bi₂Ti₄O₁₁ ceramics were investigated. The results show that ceramics sintered at 1,075–1,175 °C are single phase of Bi₂Ti₄O₁₁ and present two different sizes of prismatic shape grains. Smaller size crystals grow into larger ones with increasing sintering temperature. The ceramics sintered at 1,125 °C reach a maximum density and have a microwave dielectric properties of ε_r = 51.2, Q × f = 3,050 GHz and τ_f = ?297 ppm/°C.     

Effects of sintering aid CuTa2O6 on piezoelectric and dielectric properties of sodium potassium niobate ceramics

In this study, the effects of a sintering aid CuTa₂O₆ (CT) on (Na_0.5K_0.5)NbO₃ (NKN) ceramics were investigated. The diffracted angles in XRD profiles decreased because the Nb-sites were replaced by Cu and Ta ions, causing the expansion of lattice volume. SEM images showed smaller grain sizes at a low concentration of CuTa₂O₆, and grain sizes increased as the concentration of CuTa₂O₆ doping increased because of a liquid phase formed. When CuTa₂O₆ dopants were doped into NKN ceramics, the T_O–T and T_c phase transitions decreased because the replacement of Ta⁵⁺ ions in the B-site. A high bulk density (4.595 g/cm³) and electromechanical coupling factor (k_p, k_t) were enhanced when CT dopants were doped into NKN ceramics. Moreover, the mechanical quality factor (Q_m) also increased from 67 to 1550. NKN ceramics with sintering aid CuTa₂O₆ doping showed excellent piezoelectric properties: k_p: 42.5%; k_t: 49.1%; Q_m: 1550; and d₃₃: 96 pC/N.     

Structural and dielectric properties of complex PLZT ceramics

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Low-temperature sintering and microwave dielectric properties of Li2TiO3 based ceramics

New low sintering temperature and temperature-stable low-loss ceramics based on Li₂TiO₃ with lithium zinc borate (LZB) glass and LiZnNbO₄ doping have been prepared by the conventional solid-state reaction route. The effect of LZB glass addition on the sinterability, phase purity, microstructure, and microwave dielectric properties of Li₂TiO₃ ceramics has been investigated. The XRD results suggest the presence of single Li₂TiO₃ phases for LZB glass-added Li₂TiO₃ ceramics. The addition of LZB glass can effectively lower the sintering temperature to 900 °C, and does not induce much degradation of the microwave dielectric properties. Typically, the 2.0 wt% LZB glass-added ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 23.2, Q × f = 38,909 GHz, and τ _f  = 30.1 ppm/°C. Meanwhile, LiZnNbO₄ compound is selected to tune the temperature coefficient of resonant frequency (τ _f ) to near zero. It is found that the 2.0 wt% LZB glass-added Li₂TiO₃ ceramics with 35 wt% LiZnNbO₄ sintered at 925 °C have good microwave dielectric properties of ε_r = 20.7, Q × f = 19,366 GHz, τ _f  = ?0.5 ppm/°C, which can find applications in microwave devices that require low sintering temperature.     

Preparation and dielectric properties of BaTiO3-based X8R ceramics co-doped with BIT and CBS glass

The effects of Bi₄Ti₃O₁₂ (BIT) on phase purity and dielectric properties of BaTiO₃ (BT) ceramics have been investigated. Results show that BT samples doped with 1–3 mol% BIT adopt a single phase. However, secondary phase Bi₂Ti₂O₇ is observed when BIT content exceeds 3 mol%. Tetragonality and the Curie temperature (T _C) firstly increase and then decreases with an increase in BIT content. The 3 mol% BIT-doped BT ceramic sintered at 1,250 °C exhibits good dielectric properties of ε_r = 2,692, tan δ = 0.0152, ρ_v = 5.8 × 10¹² Ω cm, and the variation of dielectric constant as compared with that at room temperature is about ?20 % at ?55 °C and less than 11 % at 150 °C. It is found that the addition of calcium borosilicate glass (CBS) in BT-BIT ceramics can effectively lower the sintering temperature from 1,250 to 1,050 °C and further enhance the capacitance temperature stability. The permittivity decreases with an increase in CBS content from 1 to 10 wt%. Secondary phase BaBi₄Ti₄O₁₅ exists in the CBS doped BT-3BIT systems. All of CBS doped samples satisfy the X8R specification. Typically, the sample with 3 wt% CBS has ε_r = 1,789, tan δ = 0.0115, ρ_v = 9.67 × 10¹² Ω cm. The variation of permittivity as compared with that at room temperature is about ?12 % at ?55 °C and less than ± 11 % at 150 °C. The as-prepared materials have great potential as EIA X8R-type multilayer ceramic capacitors.     

ZnO掺杂对CLST微波介质陶瓷烧结及介电性能的影响

研究了烧结助剂ZnO对CaO-Li2O-Sm2O3-TiO2(简写为CLST)系微波介质陶瓷的烧结特性及介电性能的影响.结果表明:ZnO的添加能有效地降低CLST陶瓷的烧结温度至1150℃.掺杂2wt%ZnO的CLST陶瓷取得了较好的介电性能:εr=84,tanδ=0.009,τf=-15ppm/℃.     

Effects of borosilicate glass addition on the structure and dielectric properties of ZnTiO3 ceramics

ZnTiO₃ powders and borosilicate glass were made by sol-gel method, and then mixed for co-firing at low temperatures. The results show that the borosilicate glass was liquefied to improve the density of the ceramic during sintering. However, Zn₄O(BO₂)₆ and TiO₂ were formed if too much borosilicate glass was added (over 10 wt.%). The microwave dielectric properties of the ZnTiO₃ co-fired with borosilicate glass were also improved dramatically. With 5 wt.% borosilicate glass addition, ZnTiO₃ ceramics can be sintered at 850 °C and shows excellent microwave properties: 22.2 for dielectric constant, and 52,460 for Q × f value at a frequency of 6 GHz.     

Ti4+取代Zn2+、Nb5+对Bi2O3-ZnO-Nb2O5系介质材料结构和性能的影响

研究了Ti4 取代Zn2 ,Nb5 对Bi2O3-ZnO-Nb2O5系介质材料结构和性能的影响，研究表明，少量替代对于材料的结构和性能没有太大的影响；随着替代量的增加，相结构中出现正交Bi4Ti3O12相；微观形貌中出现棒晶，介电常数逐渐增大，温度系数逐渐向负温度系数方向移动，适量Ti4 替代可以获得性能很好的NP0介质材料。     

Photoelectrochemical properties of MgTiO3 and other titanates with the ilmenite structure

The photoelectrochemical properties and the diffuse reflection spectrum of MgTiO₃ are reported. MgTiO₃ shows an optical absorption edge' near 3.7 eV. This makes the material unsuitable for solar energy applications. The diffuse reflection spectra of CoTiO₃ and MnTiO₃ are presented. The optical absorption edge shifts to lower energy due to the occurrence of Me²⁺ → Ti⁴⁺ charge-transfer transitions. For various reasons discussed no photocurrents were observed for CoTiO₃ and MnTiO₃.     

Formation and structural characterization of potassium titanates and the potassium ion exchange property

In the present work, K₂Ti₂O₅, K₂Ti₄O₉ and K₂Ti₆O₁₃ are synthesized by solid state method. Their structures and morphologies are characterized by X-ray diffraction, Raman spectra and scanning electron microscopy. The binding energies of K, Ti and O in potassium titanates were then evaluated by X-ray photoelectron spectroscopy and compared with those in K/TiO₂. Finally the corresponding K ion exchange properties are investigated by synthesizing NO oxidation catalysts with Co(NO₃)₂ precursor. It is found that the binding energy of K in K₂Ti₂O₅ is much higher than those in K₂Ti₄O₉and K₂Ti₆O₁₃, and because of which, it shows quite different catalytic performances. Compared with other potassium titanates, the K in K₂Ti₂O₅ is much easier to be exchanged out.