Research of Colossal Magnetoresistance in La_(0.67)Ca_(0.33)Mn_(1-x)Cr_xO_3 (0.00x0.15)

Inthelastfewyears ,agreatdealofworkhasbeendevotedtothemixed valencemanganitesLn1-yAyMnO3(Ln =rareearthelements ,A =Ca ,Sr ,Ba)exhibitingcolossalmagnetoresistance (CMR ) [1～ 3] .Aprominentfeatureofthesematerialsisametallic insu latingtransitionassociatedwiththeferromagnetic paramagnetictransition .Earlyworkhadrevealedthesignificanceofthedouble exchangeinteractionthroughMn3 O Mn4 networkintheclosecorrelationbe tweenthetransportandthemagnetism[4 ,5] .However ,recentdetailedstudieshaves…     

Transport Properties of Rare Earth Manganese Oxide La_(0.67)Ca_(0.33)Mn_(1-x)Fe_xO_3

CompoundsofthetypeLn1-xAxMnO3(Ln =rareearth ,A =Ca ,Ba ,Sr ,etc .)havebeenthepopularsubjectsofextensiveresearchrecently ,mainlyduetotheexistenceofcolossalmagnetoresistance(CMR ) [1～ 3] .Atroomtemperature ,theperovskitecompoundLnMnO3isantiferromagneticinsulatorwhereMnistrivalent .ThepartialsubstitutionoftrivalentLnionswithdivalentionssuchasCa ,Ba ,Sr ,andPbetc .yieldsanewcompoundexhibitingstrongferro magnetismandhighmetallicconductivity .Thetrans portpropertyinthesecompoundscanbepartly…     

Luminescence Properties of (Y, Gd)Al_3(BO_3)_4∶Eu ~(3 ) under VUV excitation

Thephosphorsasanimportantpartofplasmadis playpanel (PDP)deviceemitvisiblelightundervac uumultraviolet (VUV)excitationof 14 7nmand/or172nmfromXe/Hegasplasma[1] .Untilrecently ,Y2 O3∶Eu3 and (Y ,Gd)BO3∶Eu3 havebeenusedascommercialred emittingphosphorsforPDP[2 - 3] .Butthesematerialsstillhaveshortcomingstobeim proved :lowlightoutputofY2 O3∶Eu3 uponVUVex citationandbadcolorpurityof (Y ,Gd )BO3∶Eu3 [4～ 5] .AluminoborateshavestrongabsorptionintheVUVregion ,andexhibitexcellentma…     

Luminescence and Defect Properties of Novel Bluish-Green Phosphor β-Zn_3(PO_4)_2∶Zr~(4 )

Duringlastdecade ,manyresearchershaveshowngreatinterestinluminescencepropertiesofcompoundscontainingM4 ions (M =Ti ,ZrandHf)withtheclosed shell (nd0 )becausetheyhavemorepracticalandpotentialapplications ,suchasphosphorusedinX rayintensifyingscreenandapromisingmaterialap pliedinfracturedetectionsystemofstructureceramicsinthefieldofengineeringmaterials[1,2 ] .Theopticaltransitionsinthesecompoundsareoftheligand -to -metalchargetransfer (LMCT)type .WithinthemtheZr4 -O2 chargetransfertran…     

Er~(3 ) Doped BaTiO_3 Optical-Waveguide Thin Films Elaborated by Sol-Gel Method

Bariumtitanate (BaTiO3)isawell knownferro electricmaterial.Comparedtootherferroelectricma terials,suchasLiNbO3,BaTiO3hasmanyadvancedproperties ,forexamplehighelectro opticalindex (r= 82 0pm·V- 1,6 32 8nm ,higherthan 30 8pm·V- 1at 6 32 8nmofLiNbO3) ,lowhalf wavevolt age (310Vat 6 32 8nm ,lowerthan 2 94 0Vat 6 32 8ofLiNbO3) [1] ,lowpropagatinglossofopticalwave(≤ 4± 2dB·cm- 1) [2 ] andconvenientdopingofrare earthions ,whichisnecessaryforopticallyactivede vices .RecentlyBaTiO3fi…     

两种丙烯酸盐[Ln2(CH2CHCOO)6·3H2O]·3H2O(Ln=Ce;Nd)的单晶结构

采用X射线单晶衍射法,解析了[Ln2(CH:CHCOO)6·3H2O]·3H2O(Ln=Ce;Nd)的结构.结果表明标题化合物属同构:属单斜晶系(空间群P2(1)/c);[Ce2(CH2CHCOO)6·3H2O]·3H2O晶胞参数α=1.02099(13)nm,b=1.52294(19)nm,c=2.0325(3)nin,/3=100.838(2)°,V=3.1039(7)nm3;[Nd2(CH2CHCOO)6·3H2O]·3H2O晶胞参数α=1.01978(8)nm,6=1.50979(12)nm,c=2.02712(16)nm,β=100.881(1)°,V=3.0650(4)nm3.化合物不对称结构单元中含有两个独立的稀土中心离子,分别处九、十配位环境中.两个稀土离子由两个独立的丙烯酸μ2-氧桥联形成左手和右手螺旋链.螺旋链通过链间的水分子形成氢键网络,堆垛成三维结构.     

A New Combustion Process for Nanosized BaCe_(0.95)Y_(0.05)O_(3-δ) Powders

ABO3perovskite typeoxidesdopedwithsometrivalentcationsarenowwellknownashightempera turetypeprotonconductorswithhightransportnumberofprotons .Especially ,theserareearthelement dopedABO3perovskiteoxideswithA =Ca ,Sr ,Ba ,B =Ce ,Zr ,andTi ,etc .havebeenstudiedindetail[1～ 4 ] .Suchperovskitematerialshavereceivedgreatinterestinmanyapplicationareassuchasfuelcells ,sensors ,steamelectrolyzers ,hydrogenseparationfromhydro gencontaininggasmixturesandmembranereactorsforthetransportofprotons[5～ 8]…     

Luminescence and Energy Transfer Properties of Ca_2Gd_8(SiO_4)_6O_2∶A(A=Pb~(2 ), Tm~(3 ))Phosphors

Compoundswiththeapatitestructureareverysuit ablehostlatticesforvariousluminescentions .ThemostwellknownexampleisSb3 andMn2 coactivatedcalci umhalophosphateCa5(PO4 ) 3(F ,Cl)∶Sb ,Mn ,whichhasfoundapplicationsinfluorescentlampsforalongtime[1] .Ca2 R8(SiO4 ) 6 O2 (R =Y ,Gd ,La)isakindofternaryrare earth metalsilicatewiththeoxyapatitestructure ,whichhasbeenusedashostmaterialsfortheluminescenceofvariousrareearthandmercury likeions[2～ 4 ] .Themostprominentstructuralcharacteristicisthetwos…     

Study on Spectra of La_2CaB_(10)O_(19)∶Eu~(3 ) in VUV-VIS Range

Manyboratesareexcellenthostsforrareearthlu minescence ,forexample ,nowbestredphosphorinplasmadisplaypanel (PDP )is (Y1-xGdx)BO3∶Eu[1] .Boratephosphorsdopedwithrareearthionshavebeenrichlystudiedinthepastfewdecades[2 ,3] .RecentlyWuYichengetal .[4 ] synthesizedanewbo rateLa2 CaB10 O19,whichispotentialnonlinearopticalmaterials.InthisworkweselectedLa2 CaB10 O19ashostofluminescencematerialsbecauseitprobablyisabetterhostforrareearthluminescence .Duetotherequirementofplasmadisplaypenal(PDP)…     

Preparation and Characterization of Red Luminescent Ca_(0.8)Zn_(0.2)TiO_3∶ Pr~(3+), Na~+ Nanophosphor

Pr dopedalkalineearthmetaltitanateswithper ovskitestructurehaverecentlybeenthesubjectof manyinvestigations.Thisisbecauseoftheirhigh chemicalstability,strongandsharpredemission,and longafterglowluminescence[1～13].CaTiO3∶Pr3+,asa relativelynewluminescencematerialofthatcategory,andexhibitsredcathodoluminescencelocatedatthe CIEcoordinate[8]ofx=0.680andy=0.311,very closeto“idealred”ofNTSC(NationalTelevision StandardsCommittee).Inaddition,itisapromising redlongpersistencephosphor,whichmayp…     

Photoluminescence of Dy~(3 ) Ions in Ba_3La(BO_3)_3

Dy3 isanimportantactivator .Ithasbeenexten sivelyappliedinmanyluminescentmaterials .Inre centyears ,someresearchershavestudiedthespec trumcharacteristicsofluminescentmaterialsdopedDy3 [1～ 6 ] andhaveobtainedsomemeaningfulre sults .InordertodevelopnewfluorescentmaterialsanddiscussthephotoluminescentruleofDy3 inthecomplexborate ,thispaperstudiesthephotolumines centcharacteristicsofDy3 inBa3La(BO3) 3host ,anddiscussestheinfluenceofthecharge to radiusratio(z/r)ofrareearthionRE3 andthecon…     

Polynuclear Lanthanoid Complexes Containing Aluminium—The Structure of[HoAl(CF_3COO)_2(CF_3CHOO)(C_2H_5)_2(C_4H_8O)_2]_2 at 233K

[HoAl(CF_3COO)_2(CF_3CHOO)(C_2H_5)_2(C_4H_8O)_2]_2,Mr=1468.7,monoclinic,P 2_1/n,a=1.0084(4),b=1.8453(6),c=1.4501(6)nm,β=102.40(3)°,V=2.6355(1)nm~3,Z=2,D_c=1.81gcm~(-3),F(000)=1511,T=233K,Mo Kα radiation(λ=0.071069nm).R=0.052 for 6176 unique reflections[Ⅰ≥36(Ⅰ)].The structuralunits consist of dimeric molecules with the mixed ligand and central bimetallic atoms,which are polynuclearlanthanoid complexes containing aluminium.Ho-Ho'distance is 0.3619(1)nm.The coordination polyhedron ofHo can be described in terms of a distored bicap-prism.     

Study on Luminescence Properties and Crystal-Lattice Environment of Eu~(2 ) in Sr_(4-x)Mg_x Si_3O_8Cl_4∶Eu~(2 ) Phosphor

ChlorosilicatecrystalmaterialM4 Si3O8Cl4 (M =Ba ,Sr ,Ca)isasuitablehostlatticeforluminescencematerials .Adivalenteuropiumactivatedstrontiumchlorosilicatephosphorisakindofgoodblue greenemissionphotoluminescencematerialunderUVexcita tion .Itsluminescencepropertiesandcrystalstructurehavebeenintensivelystudied[1～4 ] .Inthechlorosili catehost ,theluminescenceofEu2 consistsofa4f6 5d1- 4f7(8S7/2 )broad bandemission ,whichbe longstoelectric dipoleallowedtransitionandhasthepropertiesoflargeabso…     

二相复合体La_(2/3)Ca_(1/3)MnO_3/xCuO的界面效应

用固相反应法制备二相复合体La2/3Ca1/3Mn O3/x Cu O(x=0,0.04,0.08,0.12,0.20,0.30)。用X射线衍射(XRD)图谱、扫描电子显微镜(SEM)照片检测样品的结构,通过零场冷和加场冷的电阻率-温度(ρ-T)曲线、磁电阻-温度(MR-T)曲线研究界面效应对电输运性质及磁电阻的影响。结果表明:样品形成完好的钙钛矿相和Cu O相;复合样品的颗粒比较均匀,颗粒大小约2μm,界面比较清晰;复合样品的ρ-T曲线出现双峰,x=0.04的样品电输运性质出现反常,它的电阻率既小于x=0的电阻率,也小于x=0.08的电阻率;复合样品的MR-T曲线也出现双峰,x=0.20,0.30的样品,0.8 T磁场下在50~250 K温区磁电阻不小于13.4%,实现了大温区且有较高磁电阻,有利于MR的实际应用。用影响电输运的多种因素的竞争很好地解释了界面效应。     

A Study of Two-Phase Nanocrystalline Nd_(8.5)Fe_(75)Co_5Cu_1Zr_3Nb_1B_(6.5)Permanent Magnet

Materialswithenhancedremanentmagneticpo larizationwereinitiallypreparedbyCoehoorn[1] frommelt spunNd3.8Fe77B19.2 ribbonsbyheattreatment .Thesimilarbehaviorwasalsoobservedfrommelt spuntwo phasesamplesofNd2 Fe14 Bandα Fe[2 ] .Themag neticpropertiesofisotropicnanocrystallinetwo phasepermanentsdependsensitivelyonmicrostructuralfea tures,suchasdistributionofmagneticallyhardandsoftphases ,meangrainsize ,particleshapeandgrainboundarytype[3] .Inordertoobtainhighmaximumenergyproduct ,itisnecessaryt…     

测量与控制(六)

问题 1.电工学 图示线路中,已知Ⅴ=16V,Ⅰ=40mA,R_A=10Ω,问Rx的阻值应是多少? 2.可靠性 设备的MTBF(平均故障间隔时间)=2000小时,MTTR(平均修理时间)=5小时,问设备的利用率应是多少? [Ⅰ]99.9％;[Ⅱ]99.75％;[Ⅲ]99.6％;[Ⅳ]99.5％;[Ⅴ]99.99968％。     

晶体管高频功率放大器偏压E_B判别式的应用——验证i_(Cmax)=2 2~(1/2)Ic的合理性(E_B判别式的逆应用)

一、E_B=V_D-i_C_(max)/S·cosθ/1-cosθ判别式在不同形式脉冲作用时的表现形式 E_B=V_D-i_C_(max)/S·cosθ/1-cosθ (1) 式(1)是在i_C为类顶脉冲时得到的。尽管临界状态是最佳状态已为多数人所接受,但在某些特殊情况来看,如资料[1]中关于电报工作方式的二十二个设计举例,无疑是尖顶脉冲采用最多(约占91％),但也有用平顶脉冲工作的。资料[3]中关于平顶脉冲的分解,其基本点是一个通角为θ的大尖顶脉冲,削去其     

(La1-xPrx) 2/3Sr1/3CoO3 的成相过程与电导性能研究

采用固相反应法合成了(La1-xPrx) 2/3Sr1/3CoO3 (x=0.2,0.4,0.6,0.8) 双稀土氧化物系列粉体,研究了(La0.6Pr0.4) 2/3Sr1/3CoO3的成相过程和电导性能.结果表明,在实验过程中首先出现了La2O(CO3)和La2SrOx相,而La2SrOx相在270℃～910℃的较大范围内一直存在,再经过两次吸热到910℃时出现了(La0.6Pr0.4) 2/3Sr1/3CoO3 晶相,当温度达到1000℃时,(La0.6Pr0.4) 2/3Sr1/3CoO3 成为主晶相,在1250℃下烧结2h后,样品已成单一钙钛矿结构(La0.6Pr0.4) 2/3Sr1/3CoO3相.(La1-xPrx)2/3Sr1/3CoO3(x=0.2,0.4,0.6,0.8)双稀土氧化物的电导率在700℃附近时出现最大值,其中(La0.8Pr0.2) 2/3Sr1/3CoO3的电导率在中温范围内最大,适合作为中温固体氧化物燃料电池阴极材料.     

Effective regulation of electronic structures and luminescence properties of LiGd9(SiO4)6-x(GeO4)xO2:Dy3+ phosphors by tetrahedral substitution

A series of Dy³⁺-activated phosphors with the general formula LiGd₉(SiO₄)_6-x(GeO₄)_xO₂:Dy₃₊(0 ≤ x≤ 3)characterized by an apatite-type structure were successfully synthesized via a simple solid-state technique involving a partial substitution of [SiO₄]^4-with [GeO₄]^4- species.The effects of homovalent[GeO₄]^4--[SiO₄]^4- substit...     

复合钙钛矿型Ba[(Co_(1-x)Mg_x)_(1/3)Nb_(2/3)]O_3基微波陶瓷的结构与性能

采用传统固相法制备复合钙钛矿型Ba[(Co_(1-x)Mg_x)_(1/3)Nb_(2/3)]O_3(0.0≤x≤0.4)微波陶瓷。通过介电性能测试,结合X射线衍射仪、拉曼光谱、透射电镜等表征手段,系统研究Mg掺杂对Ba(Co_(1/3)Nb_(2/3))O_3微波陶瓷的B位1:2有序度与性能的影响。结果表明,Mg掺杂能显著提高Ba(Co_(1/3)Nb_(2/3))O_3陶瓷的B位1:2有序度,进而提高材料的品质因子。1 420℃下烧结的掺杂量x=0.2的陶瓷有序度最高,在1 300℃退火24 h后,其B位1:2有序度进一步提高,并且第二相得以消除,获得与传统Ta基复合钙钛矿微波陶瓷相当的微波性能:介电常数ε_r=30.94,品质因子Q·f=63 161 GHz,谐振频率温度系数τ_f=4.1 ppm/℃。