Sm2O3掺杂BaTiO3陶瓷的结构与电性能研究

采用溶胶-凝胶法制备了掺杂不同浓度Sm2O3(分别为0.001,0.002,0.003,0.005,0.007mol)的BaTiO3陶瓷,并对其结构与电性能进行了研究.结果表明:Sm2O3掺杂BaTiO3陶瓷的晶型在室温下为四方相,而且随着Sm2O3掺杂浓度的增加,BaTiO3陶瓷的晶粒尺寸变小,说明Sm2O3掺杂对BaTiO3陶瓷晶粒的生长有一定的抑制作用;Sm2O3掺杂BaTiO3陶瓷的电阻率比纯BaTiO3陶瓷明显下降,当添加量为0.001mol时,电阻率最小,.从4.3×109Ω·m下降为6.536×103Ω·m;Sm2O3掺杂BaTiO3陶瓷的晶粒电阻随着温度的变化,呈现NTC效应,而晶界电阻随着温度的变化,呈现PTC效应,且晶界电阻远远大于晶粒电阻,说明该材料的PTC效应是由晶界效应引起的.     

Dy掺杂BaTiO3陶瓷的制备及其介电性能

采用溶胶凝胶法制备了掺杂不同量Dy2O3(掺杂摩尔分数分别为0.001,0.002,0.003,0.005,0.007)的BaTiO3陶瓷,并对其介电性能的变化进行了研究.结果表明Dy2O3掺杂使BaTiO3陶瓷的电阻率明显降低,当添加量为0.005mol时,电阻率最小,为4.19×108Ω·m.Dy2O3掺杂使BaTiO3陶瓷的介电性能在不同掺杂量和不同频率下发生了明显变化,掺杂量为0.001mol、0.002mol时,BaTiO3陶瓷的介电特性和频率特性得到明显改善,在频率为1000Hz时介电性能相对较好.Dy2O3掺杂使BaTiO3陶瓷的介电温谱有所展宽,且Curie温度有所降低,交流电导随着温度的升高而增大,并在Curie点附近达到最高.     

ZnO-Nb2O5掺杂SnO2基陶瓷研究

通过常压烧结制备SnO2基陶瓷,研究了ZnO、Nb2O5单掺杂及ZnO-Nb2O5复合掺杂对SnO2基陶瓷的烧结性能及电阻率的影响。采用SEM及XRD对试样分别进行了微观结构观察及物相分析。研究表明,掺杂ZnO能提高陶瓷的体积密度,但对于降低电阻率的影响不明显,当ZnO掺杂量在0.5%～0.75%(质量分数)时,SnO2基体积密度可达到6.67～6.73g/cm3;掺杂Nb2O5不能有效提高烧成陶瓷的体积密度,但能显著降低SnO2基陶瓷的电阻率;0.5%(质量分数)ZnO～1.5%(质量分数)Nb2O5复合掺杂在1450℃下烧成的陶瓷可得到较好的性能,其体积密度可达到6.61g/cm3,常温电阻率为867.84Ω.cm。     

BaTiO3-Nb2O5-Ni2O3三元系统的介电性能研究

对三元系统BaTiO3-Nb2O5-Ni2O3的微结构和介电性能进行了研究．XRD分析表明Nb2O5／Ni2O3协同掺杂的BaTiO3陶瓷为赝立方相结构；在掺杂1．0mol％Ni的BaTiO3中，Nb的固溶度〈4．0mol％．SEM观察表明，随Nb掺杂量的增加，BaTiO3陶瓷的晶粒尺寸先增大后减小．BaTiO3陶瓷的室温介电常数、介质损耗，以及在低温端和高温端的电容变化率都随Nb含量的增加而先增大后减小．DSC测量表明，Nb掺杂使BaTiO3陶瓷的居里温度向高温方向移动．该系统瓷料介电性质的变化与材料的晶粒尺寸以及掺杂剂导致的相变温度的移动密切相关．本实验在BaTiO3-Nb2O5-Ni2O3系统中开发出了新型的X8R材料，这种材料很有希望用于制备大容量X8R多层陶瓷电容器．     

V2O5对 BaTiO3-Y2O3-MgO陶瓷性能的影响

研究了V2O5掺杂BaTiO3-Y2O3-MgO系陶瓷的显微结构和介电性能．SEM显示V2O5会促进该体系晶粒生长，降低陶瓷致密度．XRD显示V掺杂样品均为单一赝立方相，其固溶度〉1．0m01％．研究表明，V离子能有效抑制掺杂离子Y、Mg向BaTiO3晶粒内扩散，改变掺杂离子在晶粒中分布，从而形成薄壳层的壳芯晶粒，因此V能提高居里峰的强度并改善电容温度稳定性．多价V离子在还原气氛中以＋3、＋4为主，能增强瓷料的抗还原性，提高绝缘电阻率（10^13Ω·cm）、降低介电损耗（0．63％）．该体系掺杂0．1mol％V时，介电常数达到2600，满足X8R标准．     

BaTiO3基PTCR陶瓷中B2O3蒸汽掺杂的异常行为

钛酸钡基半导化陶瓷中的PTCR效应通常与材料中的施受主掺杂密切相关。在高温下B2O3具有较高的蒸汽压,通过B2O3蒸汽掺杂的研究表明,含主族元素B的氧化物蒸汽掺杂,钛酸钡基半导化陶瓷样品的升阻比同样得到了大幅度提高,同时室温电阻率也有所增加。B2O3蒸汽掺杂BaTiO3基材料的PTCR效应的提升可能得益于硼填隙和钡缺位相关的复合缺陷在晶界上的形成。     

B2O3蒸汽掺杂的中低温烧结Y-BaTiO3及其PTCR特性研究

通过B2O3蒸汽掺杂,Y-BaTiO3陶瓷的烧结温度大幅度降低．B2O3蒸汽掺杂后的样品,室温电阻率下降,升阻比提高．通过对氧化硼蒸汽掺杂样品的XRD分析研究表明,硼间隙可以在钛酸钡晶格中存在,硼间隙和／或相关缺陷络合物可以形成电子捕获中心,从而提高PTCR效应．     

BaO-B_2O_3-SiO_2玻璃助剂中SiO_2对低温烧结PTCR陶瓷性能的影响

研究了氧化钡-氧化硼-氧化硅(BaO-B2O3-SiO2)玻璃助剂对Y掺杂BaTiO3陶瓷微观结构和PTCR特性的影响.微观结构分析表明.玻璃助荆中SiO2的含量能改变晶界相组成,影响样品的烧结特性和室温电阻率.实验结果表明,当含有5%SiO2(摩尔分数)的BaO-B2O3-SiO2玻璃助剂的添加量为3%(质量分数)时,在1050℃保温3h烧结的样品的室温电阻率为210Ω·cm,升阻比为3.5个数量级.     

铈掺杂Ba0.1Sr0.9TiO3的改性研究

铈掺杂Ba0.1Sr0.9TiO3陶瓷有着较高的介电常数和较低的压敏电压,但其烧结温度高,烧结成功率低,非线性系数小。用ZnO和过量TiO2加以改性,研究表明:适量TiO2起到了烧结助剂的作用,可将样品的烧结温度降低到1325℃,提高了样品烧结率,钛与锶的最佳物质的量比为5∶3;ZnO作为受主掺杂剂将样品的非线性系数提高到10以上,降低了介电损耗,其最佳的掺杂量为0.7%(摩尔分数)。最后用扫描电镜分析了掺杂ZnO样品的微观形貌。     

Pr, Mn多元渗对 BaTiO3陶瓷结构与电性能的影响

采用溶胶-凝胶法制备了纯BaTiO3、Pr,Mn液相掺杂及气相多元扩渗改性的BaTiO3陶瓷.研究结果表明,Pr掺杂能使纯BaTiO3陶瓷的室温电阻率下降为1.01×10^5Ω·m;而Mn掺杂使室温电阻率升高为1.50×10^13Ω·m.但Pr和Mn的气相扩渗都能降低BaTiO3陶瓷的室温电阻率至1.08×10^3Ω·m和1.29×10^5Ω·m.Pr-Mn共渗BaTiO3陶瓷出现了典型的NTC效应.XRD分析表明,Pr或Mn掺杂并不能改变BaTiOa陶瓷的物相结构,但经Pr-Mn共渗后,出现了新化合物BaMn0.12Al1.88O4和Al8Mn4Pr的特征峰.XPS分析表明,气相多元渗使Pr,Mn,C元素都扩渗到陶瓷体内,并使各化学元素之间的结合更加牢固.SEM测试结果表明,Pr,Mn气相扩渗使陶瓷表面明显改观,晶粒生长完整,粒度分布均匀,气孔率下降.     

Thermal characterization of KClO3 KBrO3 and KIO3

The specific heats, thermal decompositions and thermal properties of the phase transitions in KClO₃ KBrO₃ and KIO₃ crystals were measured. The thermal stability of the compounds decreased in the order KIO₃ > KCIO₃ > KBrO₃. Over the temperature range 250–600 K, no phase transitions were detected for KBrO₃: one at 545 K for KClO₃ and two for KIO₃ at 345 and 487 K.     

Flux growth of single magnetic sublattice antiferromagnetic garnets Ca3 Fe2 Ge3 O12 and Ca3 Mn2 Ge3 O12

Magnetic single crystals garnets Ca₃ X₂ Ge₃ O₁₂ with X = Mn³⁺ or Fe³⁺ containing Ca²⁺ and Ge⁴⁺ are of great interest due to the rise of an antifer-romagnetic order in one definite octahedral site. The optimal conditions for obtaining single magnetic-sublattice garnets of large size (1 cm in diameter) have been analyzed. Two groups of solvents have been tested: Bi₂ O₃ or PbO based flux. The best results were obtained with PbO flux and starting composition : % Moles 44 PbO 1b 35 GeO₂ 1b 15 CaO 1b 6 X₂ O₃.     

Hydrothermal Crystallization in the Systems La2(CO3)3 ? 6H2O-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaHCO3, KHCO3, NaCl, NH4Cl, CO(NH2)2)

Crystallization in the systems La₂(CO₃)₃ ⋅ 6H₂O-CaCO₃(BaCO₃)-R-H₂O (R = Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, NaCl, NH₄Cl, CO(NH₂)₂) was studied under hydrothermal conditions (400–450°C). The solid reaction products were found to contain LaOHCO₃ and NaLa(CO₃)₂. Detailed thermal decomposition schemes were proposed for these phases, and their lattice parameters were refined. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 11, 2005, pp. 1366–1372. Original Russian Text Copyright ? 2005 by Nikol'skaya, Dem'yanets.     

Electrical properties of sintered EuZrO3  EuNbO3 and EuNbO3

Electrical resistivity of two-phase products [yEuZrO₃ + (1 ? y) EuNbO₃] increased continuously with y, and a transition from a metallic to semiconducting characteristic occured at y = 0.14. The resistivity varied almost linearly with temperaure in the range y = 0 to y = 0.24, and thermal coefficients of resistivity at 300 K for the products decreased from +5.9 × 10^?4 K^?1 to ?7.4 × 10^?4 K^?1 according to the value of y. At y = 0.14, the thermal coefficient was almost zero. Thermal coefficients of electrical resistivity for the niobates with various oxygen contents were all positive in the range $\text{2.55 <}\text{O}\text{Nb}\text{< 3.24}$ and exhibited a sharp minimum at $\text{O}\text{Nb}\text{= 2.92}$. In all these niobates, Eu_xNbO₃ was a major phase and Eu₃NbO₆ or EuNbO₂ was detected as a second phase in the range $\text{O}\text{Nb}\text{> 3}$ or $\text{O}\text{Nb}\text{< 3}$ respectively. Peaks in the resistivity curves were correlated with a magnetic ordering temperature for samples with an overall ratio $\text{O}\text{Nb}\text{> 3}$.     

Elastic modulus and hardness of CaTiO3, CaCu3Ti4O12 and CaTiO3/CaCu3Ti4O12 mixture

Three ceramic systems, CaTiO₃ (CTO), CaCu₃Ti₄O₁₂ (CCTO) and intermediate nonstoichiometric CaTiO₃/CaCu₃Ti₄O₁₂ mixtures (CTO.CCTO), were investigated and characterized. The ceramics were sintered at 1100 °C for 180 min. The surface morphology and structures were investigated by XRD and SEM. Elastic modulus and hardness of the surfaces were studied by instrumented indentation. It was observed that CCTO presented the higher mechanical properties (E = 256 GPa, hardness = 10.6 GPa), while CTO/CCTO mixture showed intermediate properties between CTO and CCTO.     

Influence of BaZrO3, MnCO3 additives on dielectric properties and microstructure of Ba(Zn1/3Nb2/3)O3 ceramics and Ba(Zn1/3Nb2/3)O3-Sr(Zn1/3Nb2/3)O3 solid solutions

The effect of BaZrO₃, MnCO₃ additives on the dielectric properties, sintering temperature and microstructure of Ba(Zn_1/3Nb_2/3)O₃ (BZN) and Ba(Zn_1/3Nb_2/3)O₃-Sr(Zn_1/3Nb_2/3)O₃ (BSZN) ceramics was studied in this paper. It indicates that both BaZrO₃ and MnCO₃ can lower the sintering temperature of the ceramics and accelerate the crystallization of BZN and BSZN. The dielectric constant ɛ _r increases after MnCO₃ added, but decreases when BaZrO₃ added alone. The existence of MnCO₃ can modulate the temperature coefficient of capacitance τ _c toward positive, while BaZrO₃, can make c more negative. MnCO₃ and BaZrO₃ can restrain the appearance of the second phase; while BaZrO₃, can prevent the appearance of the superstructure. In the BSZN system, when 1 mass % MnCO₃ added, sintering temperature(t _s ) is lowered to 1240°C. In this study, the best sample that has the excellent properties is sample 5 with dielectric properties of ɛ _r = 43.6, τ _c = −8 × 10⁻⁶ °C⁻¹ and tan δ = 0.6 × 10⁻⁴ (1 MHz). The sintering temperature of BZN and BSZN system can be lowered to less than 1300°C.     

Deposition process of Si-B-C ceramics from CH3SiCl3/BCl3/H2 precursor

Si-B-C coatings have been prepared by chemical vapour deposition (CVD) from CH₃SiCl₃/BCl₃/H₂ precursor mixtures at low temperature (800-1050 °C) and reduced pressures (2, 5, 12 kPa). The kinetics (including apparent activation energy and reaction orders) related to the deposition process were determined within the regime controlled by chemical reactions. A wide range of coatings, prepared in various CVD conditions, were characterized in terms of morphology (scanning electron microscopy), structure (transmission electron microscopy, Raman spectroscopy) and elemental composition (Auger electron spectroscopy). On the basis of an in-situ gas phase analysis by Fourier transform infrared spectroscopy and in agreement with a previous study on the B-C system, the HBCl₂ species was identified as an effective precursor of the boron element. H_xSiCl_(4−x), SiCl₄ and CH₄, derived from CH₃SiCl₃, were also shown to be involved in the homogeneous and the heterogeneous reactions generating silicon and carbon in the coating. A correlation between the various experimental approaches has supported a discussion on the chemical steps involved in the deposition process.     

New phases in the systems EuF2:YF3 and EuF2:GdF3

Isothermal pseudo-binary phase studies of the systems EuF₂:YF₃ and EuF₂:GdF₃ have been completed at 1100°C. Three single phase regions corresponding to (1) EuF₃(ss); (a) hexagonal tysonite and (3) orthorhombic LnF₃(ss), Ln = Y, Gd, have been found. The single phase regions for both of these systems are similar and exist at 0–39, 73–82 and 91–100 mole % YF₃; 0–41, 70–77 and 85–100 mole % GdF₃.     

Dielectric properties of Pb3 (PO4)2 | Pb3 (AsO4)2

The dielectric constants of Pb₃ (PO₄)₂ | Pb₃ (AsO₄)₂ at room temperature are intrinsic and fulfill the Lyddane - Teller - Sachs relation. At higher temperatures the specific conductivity increases with an activation energy of 0.56 eV leading to Maxwell - Wagner polarization effects thereby increasing the effective dielectric constant. Corresponding peaks in ∈' (T) are extrinsic and not attributed to structural phase transformations.     

Electrical properties of Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics modified with WO3

Ferroelectrics 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (PMN-PT) + x mol% WO₃ (x=0.1, 0.5, 1, 2) were prepared by columbite precursor method. Electrical properties of WO₃-modified ferroelectrics were investigated. X-ray diffraction (XRD) was used to identify crystal structure, and pyrochlore phase were observed in 0.67Pb (Mg_1/3Nb_2/3)O₃-0.33PbTiO₃+2 mol% WO₃. Dielectric peak temperature decreased with WO₃ doping, indicating that W⁶⁺ incorporated into PMN-PT lattice. Lattice constant, pyrochlore phase and grain size contribute to the variation of K_max. Both piezoelectric constant (d₃₃) and electromechanical coupling factors (k_p) were enhanced by doping 0.1 mol% WO₃, which results from the introduction of “soft” characteristics into PMN-PT, while further WO₃ addition was detrimental. We consider that the two factors, introduction of “soft” characteristics and the formation of pyrochlore phase, appear to act together to cause the variation of piezoelectric properties of 0.67PMN-0.33PT ceramics doping with WO₃.