Nd3+A位置换对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能的影响

研究了Nd3+离子A位置换改性(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷的微波介电性能.[(Pb0.5Ca0.5)1-xNdx](Fe0.5Nb0.5)O3(PCNFN)陶瓷的微波介电性能得到改善是由于少量过剩的Nd3+与(Pb,Ca)2+的固溶能够消除氧空位.当x=0.02时,能够形成单相的钙钛矿相,随着Nd3+置换量的增加,过剩的Nd3+将导致第二相焦绿石的形成,焦绿石会恶化PCNFN的微波介电性能.PCNFN介电性能随x的增加而下降是由于焦绿石相随x增加的结果.当x=0.02-0.05,PCNFN陶瓷有很好的微波介电性能,介电常数K>100,Qf值为5385-5797GHz,频率温度系数TCF随Nd3+含量的增加从正的变为负的.     

MLnBO_4陶瓷中K_2NiF_4型层状钙钛矿结构的稳定性

通过固相反应法制备了MLnBO_4(M=Ba,Sr,Ca;Ln=La,Nd,Sm,Y;B=(Zn0.5Ti0.5),(Mg_(0.5)Ti_(0.5)))陶瓷粉末,使用X射线衍射仪(XRD)分析其相组成,并结合文献中B位为Ga和Al时的结果,探讨了MLnBO_4中K_2NiF_4型层状钙钛矿结构的稳定性。当M~(2+)和B~(3+)固定时,K_2NiF_4型结构的稳定性随钙钛矿层许容因子t偏离1程度的增加而降低;但当M~(2+)或B~(3+)改变时,两者之间并无直接联系。而考虑M~(2+)、Ln~(3+)、B~(3+)离子半径的对比时,则发现K_2NiF_4型结构均出现在以r(M~(2+))/r(Ln~(3+))=1.1、r(Ln~(3+))/r(B~(3+))=2为中心的一定范围内。因此,用M~(2+)、Ln~(3+)、B~(3+)离子半径的对比衡量MLnBO_4中K_2NiF_4型层状钙钛矿结构的稳定性远较用钙钛矿层的许容因子更可靠,这对于相关材料的设计和开发具有重要意义。     

Effect of Sn4+ B-Site Substitution on the Microstructure and Dielectric Properties of Ba(Mg1/3Ta2/3)O3 Microwave Ceramics

1.IntroductionRecent progress of microwave telecommunication de-mands the development and application of a variety ofmicrowave dielectric materials.The materials with highdielectric constant(ε),high quality factor(Q)and smalltemperature coefficient of resonant frequency(TCF)haveattracted the greatest interest of researchers.The com-pounds Ba(B'1/3B"2/3)O3(B'=Mg,Zn,Ni,etc.B"=Ta,Nb,etc.)with complex perovskite structure exhibit veryhigh Q value at microwave frequencies greaterthan10GHz.…     

Microwave dielectric properties of (A2+(1/3)B5+(2/3))0.5Ti0(0.5)O2 (A2+ = Zn, Mg, B5+ = Nb, Ta) ceramics

Dielectric properties of (A(2+)(1/3)B(5+)(2/3))(0.5)Ti0(0.5)O(2) (A(2+) = Zn, Mg, B(5+) = Nb, Ta) ceramics were investigated at microwave frequencies. A single phase with tetragonal rutile structure was obtained through the entire compositions. Dielectric properties were strongly dependent on the structural characteristics. The specimens with B(5+) = Nb showed a larger dielectric constant than those with B(5+) = Ta due to the decrease of bond valence. Quality factors (Qf) of the specimens with B(5+) = Ta were larger than those with B(5+) = Nb. Temperature coefficient of the resonant frequencies (TCF) of (Zn(1/3)Nb(2/3) )0(0.5)Ti0(0.5)O(2) was larger than that of (Mg(1/3)Ta(2/3))0(0.5)Ti0(0.5)O(2). These results could be attributed to the changes of the temperature coefficient of dielectric constant and the degree of oxygen octahedral distortion.     

Nd3+A位置换对(Pb0.5Ca0.5)(Fe0.5Nb0.5)O3陶瓷微波介电性能的影响

研究了Nd³⁺离子A位置换改性(Pb_0.5Ca_0.5)(Fe_0.5Nb_0.5)O₃陶瓷的微波介电性能.[(Pb_0.5Ca_0.5)_1-xNd_x](Fe_0.5Nb_0.5)O₃(PCNFN)陶瓷的微波介电性能得到改善是由于少量过剩的Nd³⁺与(Pb,Ca)²⁺的固溶能够消除氧空位.当x=0.02时,能够形成单相的钙钛矿相,随着Nd³⁺置换量的增加,过剩的Nd³⁺将导致第二相焦绿石的形成,焦绿石会恶化PCNFN的微波介电性能.PCNFN介电性能随x的增加而下降是由于焦绿石相随x增加的结果.当x=0.02-0.05,PCNFN陶瓷有很好的微波介电性能,介电常数K>100,Qf值为5385-5797GHz,频率温度系数TCF随Nd³⁺含量的增加从正的变为负的.     

Incorporation of lanthanide ions in lead titanate

Lanthanide ion doping of lead titanate was investigated using structural and differential scanning calorimetry measurements. Dense ceramics samples were prepared with starting compositions, Pb_1−3x/2Ln _x TiO₃, assuming A-site substitution of Ln = La, Nd, Sm, Eu, Gd and Dy, at 2 and 8 at.%. Doping with La³⁺ reduced the tetragonality and cell volume. A systematic recovery in these values was observed for the smaller Ln³⁺ ions, suggesting the onset of partial substitution of the Ln ions at the B-site. The ferroelectric–paraelectric transition temperatures also recovered, consistent with an increased probability of B-site occupation with decreasing ion size. Evidence for site occupancy obtained from the presence cation vacancies is also discussed.     

Perovskite-type oxides as susceptor materials in dielectric heating

Dielectric properties of La_1−x Ce _x MnO₃ perovskites are investigated in order to assess the heating behaviour in the wider context of the use of perovskite coatings in microwave assisted soot filter regeneration. Dielectric permittivities in the radio and microwave region for these perovskites were determined at room temperature. The dielectric constant and dielectric loss are related to ionic conduction at low frequencies, while at microwave frequencies storage and loss mainly proceed through reorientation of molecular dipoles. The dielectric constant rises for a higher degree of La substitution by Ce, which is explained by an increase of the number of cation/oxygen vacancies. Concurrently the mean perovskite crystallite size decreases, which is possibly related to defect formation. The dielectric constant declines for x ≥ 0.3, along with the formation of a separate, low dielectric permittivity CeO₂ phase. The La–Ce–Mn perovskites are further shown to exhibit a high thermal stability during repeated heating/cooling cycles.     

Structural and surface characterization of perovskite-type oxides; influence of A and B substitutions upon oxygen binding energy

Monophasic samples of seven different oxides with perovskite structure, and also -NaAlO2 have been prepared for catalytic applications. They have been characterized by X-ray diffraction and electron microscopy, then by X-ray photoelectron spectroscopy (XPS). The XPS spectra of LaAlO3, La0.9Sr0.1Al0.8Cu0.1Ru0.1O3, La0.8Sr0.2Al0.8Cu0.1Ru0.1O3 and -NaAlO2 contained only one well-defined O 1s peak. The binding energy obtained from the oxygen peak of the perovskites (529.8 eV) was, however, significantly different from that of -NaAlO2 (532.2 eV). The other perovskite oxides, La0.9Ca0.1AlO3, La0.8Ca0.2AlO3, La0.8Sr0.2AlO3 and LaAl0.8Cu0.2O3 had two more or less well-resolved O 1s peaks separated by 2.4 eV. Tentatively, we have interpreted these observations to mean that, in the latter compounds, the surface is reconstructed so that the Al3+ ions have changed their coordination from octahedral to tetrahedral. © 1998 Kluwer Academic Publishers     

ZnAl_2O_4和La_2O_3对Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷介电性能的影响

通过传统的固相反应合成掺杂ZnAl_2O_4和La~(3+)(来自La_2O_3)的Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷粉体,干压成型后在空气气氛下常压烧结制备ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品。分别研究了La~(3+)和ZnAl_2O_4的掺杂量对复合陶瓷样品的微观形貌、相组成和介电性能的影响。结果表明:ZnAl_2O_4具有细化晶粒的作用;Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷样品的致密度随La~(3+)和ZnAl_2O_4含量的增加而增加;介电常数和谐振频率温度系数随ZnAl_2O_4含量的增加而减小,随La_2O_3添加量变化不大;品质因数值随ZnAl_2O_4含量的增加先增加后减小。制备出的ZnAl_2O_4和La~(3+)掺杂Ca_(0.61)Nd_(0.26)TiO_3-MgTiO_3复合陶瓷致密度达到94%以上,介电常数在40~50之间,谐振频率温度系数小于40×10~(-6)℃~(-1),品质因数大于38 000GHz,可以用于通信技术领域。     

Magnetic and Superconducting Properties of Doped and Undoped Double Perovskite Sr<Subscript>2</Subscript>YRuO<Subscript>6</Subscript>

We report here SQUID (magnetization) measurements, along with supporting specific heat, Raman, SEM (scanning electron microscope), EDX (energy dispersive X-ray) and XRD (X-ray diffraction) measurements, on Cu-doped and undoped double perovskite Sr₂²⁺Y³⁺Ru⁵⁺O₆^2-\mathrm{Sr}_{2}^{2+}\mathrm{Y}^{3+}\mathrm{Ru}^{5+}\mathrm{O}_{6}^{2-} (abbreviated as SrY2116) system grown as single crystal using high-temperature solution growth technique. These measurements show the undoped system to be a nonmetallic (insulating) spin glass (SG) and the ∼5–30% Cu-doped (i.e. Cu-concentration/(Cu + Ru-concentration) ∼5–30%) system to be a spin glass superconductor (SGSC) with T _c (critical temperature) ∼28–31 K and superconducting volume fraction, f _sc∼2.2–9%. To mention, similar measurements done on undoped and Cu-doped BaY2116 and BaPr2116 systems show for them the same (SG, SGSC) behaviors. However they show a decrease in T _c and f _sc when diamagnetic Y³⁺ ions are replaced by Pr³⁺ spins, presumably due to enhanced internal pair breaking, and also decreased Cu–O–Cu overlap, owing to Pr³⁺ presence; these phenomena are known to exist in the Pr123 compound, PrBa₂Cu₃O_7−δ (δ∼0), due to ∼10% of Pr³⁺ ions having tendency to occupy Ba²⁺ sites. Measurements done on undoped and Cu-doped SrHo2116 show similar SG and SGSC properties. Further, the undoped and Cu-doped SrY2116 crystals grown by hydrothermal growth technique (i.e., grown using lower temperature and high pressure) show same behaviors. From these investigations it can be said that the undoped Ru-double perovskites (A₂BB′O₆, B′=Ru) are SG systems and that Cu-doped Ru-double perovskites (A₂BB′O _δ , δ∼6, B′=Ru_1−x Cu _x , 0<x≲0.3) are SG superconductors (SGSCs). Results are discussed.     

Synthesis,structural characterization and Mössbauer study of LnV0.5Fe0.5O3 perovskites (Ln = Y,La, Ce,Pr, Nd,Sm, Eu,Gd, Tb,Dy, Ho and Er)

Perovskites LnV_0.5Fe_0.5O₃ (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Er) were synthesized by rapid solidification from arc-melted samples and characterized by the study of their crystal structure and hyperfine properties. These metastable solid solutions crystallized in the Pbnm symmetry, with the iron and vanadium cations randomly distributed in the transition metal octahedral sites. Depending on the lanthanide present at the A site of the perovskite, iron is present with two valences (i.e., Fe³⁺ and Fe²⁺). The volume of the unit cell for these perovskites increases linearly with the lanthanide ionic radius, as the perovskite approaches its ideal structure. At room temperature, the quadrupolar splitting of the trivalent paramagnetic Mössbauer component works as an indirect measurement for the Goldshmidt tolerance factor. Close to or below 100 K, these perovskites undergo a crystallographic phase transformation, probably due to orbital ordering of the V³⁺ cations, originating two different magnetic iron sites.     

Dielectric Properties of Ba0.6Sr0.4TiO3-La(B0.5Ti0.5)O3 (B=Mg, Zn) Ceramics

Ba_0.6Sr_0.4TiO₃-La(B_0.5Ti_0.5)O₃ (B = Mg, Zn) ceramics were prepared by a solid-state reaction method, and their microwave dielectric characteristics and tunability were investigated. The ferroelectric-dielectric solid solutions with cubic perovskite structures were obtained for compositions of 10 to 60 mol% La(Mg_0.5Ti_0.5)O₃ and 10 to 50 mol% La(Zn_0.5Ti_0.5)O₃. With the increase of linear oxide dielectric content, the dielectric constant and tunability were decreased and Qf was increased. Ba_0.6Sr_0.4TiO₃-La(Mg_0.5Ti_0.5)O₃ has better dielectric properties than Ba_0.6Sr_0.4TiO₃-La(Zn_0.5Ti_0.5)O₃. 0.9Ba_0.6Sr_0.4TiO₃-0.1La(Mg_0.5Ti_0.5)O₃ has a dielectric constant ε = 338.2, Qf = 979 GHz and a tunability of was 3.7% at 100 kHz under 1.67 kV/mm. The Qf value of 0.5Ba_0.6Sr_0.4TiO₃- 0.5La(Mg_0.5Ti_0.5)O₃ reached 9367 GHz, but the tunable properties were lost.     

PVC membrane potentiometric sensor based on 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthroline-phane for selective determination of neodymium(III)

Spectrofluorometric studies on the binding properties of 5-pyridino-2,8-dithia[9](2,9)-1,10-phenanthrolinephane (L) toward La3+, Sm3+, Gd3+, Yb3+, and Nd3+ in methanol solution revealed the occurrence of both 1:1 and 2:1 (ligand/metal) complexation with a stability order of Nd3+ > Yb3+ > Gd3+ > Sm3+ > La3+. Consequently, L was used as a suitable neutral ionophore for the preparation of a novel polymeric membrane-selective electrode for Nd3+ ion. The electrode exhibited a Nernstian response over a wide concentration range (1.0 x 10(-6)-1.0 x 10(-2) M) with a low limit of detection of 7.9 x 10(-7) M. The electrode possesses a fast response time of <5 s and can be used for at least 9 weeks without observing any considerable deviation. The proposed electrode revealed a very good selectivity for Nd3+ over a wide variety of alkali, alkaline earth, transition, and heavy metal ions, including members of the lanthanide family other than Nd3+. The potentiometric response of the electrode is independent of the pH of test solution in the pH range 4.0-6.5. The proposed electrode was successfully applied to the recovery of Nd3+ ion from tap water samples and, also, as an indicator electrode, in potentiometric titration of neodymium(III) ions.     

Influence of A-site nonstoichiometry on sintering, microstructure and electrical properties of (Bi0.5Na0.5)TiO3 ceramics

Lead-free (Bi_0.5Na_0.5)_1+xTiO₃ ceramics (x = −0.02, −0.01, −0.005, 0, 0.005 and 0.01) were prepared by ordinary sintering. The effect of A-site stoichiometry on the densification, microstructure, dielectric properties, high-temperature impedances, and piezoelectric properties was explored. It was found that the high conductivity of (Bi_0.5Na_0.5)TiO₃ (BNT) ceramics should be mainly attributed to the formation of A-site cation vacancies during sintering. Improved physical and electrical properties can be achieved in the sample with A-site cation excess. The control of the stoichiometry proves to be an effective way to improve BNT ceramics for possible application.     

Phase Composition, Microstructure, and Thermal Expansion of B2O3-Modified LaGaO3-Based Ceramics

Data are presented on the phase relations in the La₂O₃–SrO–Ga₂O₃system and the effect of B₂O₃additions on the structure and morphology of (La,Sr)(Ga,Mg)O_{3 –} ceramics. The formation of the perovskite phase (La,Sr)GaO₃is shown to proceed through La₄SrO₇and La₂SrO_{4 +} . The unit-cell of (La,Sr)(Ga,Mg)O_{3 –} is found to vary linearly with Sr + Mg content. The introduction of boron-containing additions reduces the sintering temperature of the ceramics by up to 200°C.     

Transition metal cations extraction by ester and ketone derivatives of chromogenic azocalix[4]arenes

The molecule of azocalix[n]arene is a macrocyclic used effectively in the complexation of the heavy metal pollutants (like silver and mercury). In this work, our main aim is to prepare new chromogenic azocalix[n]arene molecules to elaborate an extractant with high extractant selectivity for metal ions able to detect this type of pollutant. The solvent extraction properties of four acetyls, four methyl ketones and four benzoyls derivatives from azocalix[4]arenes which were prepared by linking 4-ethyl, 4-n-butyl, 4-acetamid anilin and 2-aminothiazol to calix[4]arene through a diazo-coupling reaction, the alkaline earth (Sr2+) and the transition (Ag+, Hg2+, Co2+, Ni2+, Cu2+, Zn2+, Cd2+, Cr3+) metal cations have been determined by extraction studies with metal picrates. Both ketones are better extractants than esters, and show a strong preference for Ag+, while Cu2+ and Cr3+ are the most extracted cation with the esters. Both acetyl and benzoyl esters are good carriers for Ag+ and Hg2+.     

La2O3、Y2O3掺杂对(Na0.5Bi0.5)0.94Ba0.06TiO3无铅压电陶瓷性能的影响

以(Na0.5Bi0.5)0.94Ba0.06TiO3为基体,研究了单、双组分掺杂La2O3、Y2O3对BNBT6陶瓷的压电和介电性能及微观结构的影响。XRD分析表明:掺杂La2O3、Y2O3均得到钙钛矿结构。SEM分析表明,分别掺杂0.2%La2O3和0.2%Y2O3使得陶瓷晶粒增大,压电常数提高,双组分掺杂La2O3、Y2O3在掺杂量0.12%La2O3+0.08%Y2O3时,压电常数d33增大到最大值144.6×10-12C/N,介质损耗降低到最小值0.039。     

The role of dopants in tailoring the microwave properties of Ba6-xR8+2/3x Ti18O54 R = (La–Gd) Ceramics

Microwave dielectric ceramics with a high dielectric constant need to satisfy very high technical demands. They should possess extremely low losses to achieve high Q-values (Quality factor) a small temperature coefficient of resonant frequency (τf), and a relative permittivity (εr) higher than 80. Industrial applications require very stringent electrical and dimensional tolerances, typically ± 0.5–1.0 ppm K-1 for a specified τf and ± 0.25% for a specified εr. To meet such requirements ceramics based on BaO–R2O3 – TiO2 (R = La–Gd) are used. The investigation of this type of ceramic was stimulated by the observation that ceramics based on compositions in the TiO2-rich region of the system exhibit highly temperature stable electrical properties. Especially interesting are compositions within the solid solubility region with the general formula Ba6-xR8+2/3x Ti18O54. As the ionic radius of the rare earth decreases the extent of the solid solubility region becomes narrower, i.e., 0<x<3 for La and x = 0.5 for Gd. Further improvements in the dielectric microwave properties can be achieved by combining different rare earth oxides, and by partial replacement of Ba2+ with other alkaline earth atoms such as Ca2+ and Sr2+. Typically such ceramics meet the requirements for Q and εr; however, τf must be additionally adjusted by the use of dopants. Most commonly bismuth and lead oxides or titanates are used. In the present contribution the role of different dopants and their influence on the resulting microwave dielectric properties of Ba6-xR8+2/3x Ti18O54 based ceramics are discussed. This revised version was published online in November 2006 with corrections to the Cover Date.     

DFT study of the stability of oxygen vacancy in cubic <Emphasis Type="Italic">AB</Emphasis>O<Subscript>3</Subscript> perovskites

Rare earth and alkaline earth metal perovskites with general formula ABO₃ have attracted much attention as electrocatalysts for state-of-the-art fuel cells, and catalysts for hydrogen generation and hydrocarbons oxidation. Tuning the ion conductivity through doping A and B and subsequent formation of oxygen vacancies is essential for the performance of perovskites materials. To provide insights into factors that affect stability of oxygen vacancies and understand the origin of the activity of doped perovskite materials, we investigate the structure and energetics of cubic ABO₃ perovskites (A = La and/or Be, Mg, Ca, Sr, Ba; B = Ti, V, Cr, Mn, Fe, Co, and Ni) using density functional theory calculations. It is found that the lattice constant of ABO₃ generally increases as the ionic radius of A and B; the bulk formation energy of ABO₃ is decomposed into the ionization energy and lattice energy, which depend on the ionic radius and valence. The trend of bulk formation energy corresponds to that of ionization energy at a given ionic valence, while corresponds to that of lattice energy as doping La by alkali earth metals with lower valence. There exists a good linear relationship between the bulk formation energy and oxygen vacancy formation energy. This work provides an understanding toward the origin of the activity of perovskites at the atomic level.     

Novel perovskites M2IILnIIIRuVO6 as emission control catalysts

New perovskites, M₂^IILn^IIIRu^VO₆, where M^II = Ba and Sr, Ln^III = rare earths, Y and Bi, were prepared. The Ba series exhibits cubic cells for Ln^III = La to Dy and hexagonal cells for Ln^III = Yb and Y. The Sr series exhibits superlattices for Ln = La through Nd and orthorhombic distortions for Ln = Sm through Yb. Ba₂LaRuO₆ showed catalytic activity and thermal stability for the reactions: 2NO + 2CO → N₂ + 2CO₂ and 2CO + O₂ → 2CO₂. The combination of three basic cations per Ru and the perovskite structure stabilizes Ru in these catalysts.