S perconductivity What Is a Superconductor? R Brief History A superconductor is an element, inter- a Characteristic of Superconductor metallic alloy, or compound that wi electricity without resistance below a a Important Superconductors temperature. e Once set in motion. electrical current will superconducting material- making it the closest thing to perpetual motion in nature. e Superconductivity is a"macroscopic quantum Superconductivity Superconductors Compared to Other Conductors tThe temperature dependent Fewer electrons are excited from the change between superconducting and normal conductors), into the acceptor band (in type ext dThe temperature at which valence band to the conductio this drastic decrease Metol n intrinsic semiconductors) ductors show a decrease in superconductor. Fewer vibrations result in a more ro. This is the Superconducting Critical Temperature Tc Three Temperatures the temperature at which the system(sample) L Moonset)onset transition onducting state into a superconducting stat characterized by zero de electrical resistivity lation of normal resistance R a Tdmin)-the middle transition Dormal d the oint that resistance drops to rn P 骂T。 the temperature when resistance drops to zero For YBa Cu0 42K .T=905K and △Tc1K
1 Superconductivity Brief History Characteristic of Superconductors Applications Important Superconductors What Is a Superconductor? A superconductor is an element, intermetallic alloy, or compound that will conduct electricity without resistance below a certain temperature. Once set in motion, electrical current will flow forever in a closed loop of superconducting material –making it the closest thing to perpetual motion in nature. Superconductivity is a “macroscopic quantum phenomenon”. Superconductivity Materials become superconductors below some critical temperature, TC. The temperature dependent change between superconducting and normal conduction is abrupt! The temperature at which this drastic decrease in resistance occurs is the critical temperature of a superconductor. Abrupt change! Resistance goes to zero. This is the critical temperature. Superconductors Compared to Other Conductors Semiconductors show a increase in resistance as the temperature is decreased. Fewer electrons are excited from the donor band (in n-type extrinsic semiconductors), into the acceptor band (in p-type extrinsic semiconductors), and from the valence band to the conduction band (in intrinsic semiconductors). Metal conductors show a decrease in resistance as the temperature is decreased. Fewer vibrations result in a more ‘perfect’lattice. Superconducting Critical Temperature Tc = the temperature at which the system (sample) undergoes a phase transition from a normal conducting state into a superconducting state, characterized by zero dc electrical resistivity. normal superconductor Three Temperatures Tc(onset) — onset transition temperature, when the R-T curve begin to departure from the linear relation of normal resistance Rn. Tc(min) — the middle transition temperature, which correspond the point that resistance drops to Rn/2. T¥ — the temperature when resistance drops to zero. For YBa2Cu3O7-d : •Tc(onset)=95K， •Tc(min)=91K •T¥=90.5K and △Tc=1K
Discovery of Superconductivity Mercury Superconducting Transition by H. Kamerlingh Onnes (1911) historically the first to show superconduct that its critical nagnetic 019 T. so the amount =42K carry is also limited. I How the Superconductivity Was First Discovered? Superconductive Element m2m画mPHx 图图 atmosphere and the temperature increased. It was ThEN that they activity was first discovered. (Not on cooling article, there is a description that "the tap 出出其 Li: Element With the Highest Tc Materials Transition temp. (K 270°C) superconducting Nb3sn 238(249C the lightest metal of 25(148°C 135~165K ition temperature(Te of 20 K at 48GPa. This elements with low Ra reve a very high ggests that metallie hydrogen mbers will have high transition
2 Mercury Superconducting Transition Mercury was historically the first to show superconductivity. Its practical usefulness is limited by the fact that its critical magnetic field is only 0.019 T, so the amount of electric current it can carry is also limited. Discovery of Superconductivity by H. Kamerlingh Onnes (1911) How the Superconductivity Was First Discovered? (This story was told by Prof. P. Kes of Leiden in 1993 at a NATO summer school in Erice, Italy.) There were two assistants working for Onnes, Horst and Dorshman (these names need to be confirmed). The son of Dorshman told Prof. Kes in 1992 the story of the discovery of superconductivity his father used to tell to his son. They were studying the resistance of mercury with a resistance bridge. One day, by pumping on liquid He in the cryostat, they realized that for some reason the resistance bridge did not seem to be working properly because it was not giving any signal. After they stopped the pump, by mistake, they forgot to re-open the valve to release the evaporated He gas from the cryostat. The pressure increased beyond atmosphere and the temperature increased. It was THEN that they noticed that the resistance of mercury recovered! This is how the superconductivity was first discovered. (Not on cooling, but on warming mercury!) In the Leiden Communication article, there is a description that “the tap (valve) Eak2”was used to increase the temperature. Superconductive Elements Table from Burns A15 compounds alloy Materials Transition temp.(K) Al 1.2 (-272°C) Sn 3.4 (-270°C) Pb 7.2 (-266°C) Nb3Sn 23.8 (-249°C) LaSrCuO 40 (-233°C) YBaCuO 90 (-178°C) BiSrCaCuO 107 (-166°C) TlBaCaCuO 125 (-148°C) HgBaCaCuO 135 ~ 165K Li: Element With the Highest TC K. Shimizu et al., Nature 2002, 419, 587. Superconductivity at high temperatures is expected in elements with low atomic numbers. For example, it has been predicted that when hydrogen is compressed to its dense metallic phase (at pressures exceeding 400 GPa), it will become superconducting with a transition temperature above room temperature. Such pressures are difficult to produce in a laboratory setting, so the predictions are not easily confirmed. Under normal conditions lithium is the lightest metal of all the elements, and may become superconducting at lower pressures. In this work, Li shows superconducting at pressures greater than 30 GPa, with a pressure dependent transition temperature (Tc) of 20 K at 48GPa. This is the highest observed Tc of any element; it confirms the expectation that elements with low atomic numbers will have high transition temperatures, and suggests that metallic hydrogen will have a very high Tc
Superconductivity of Iron Fe) re dependence of the Superconductivity 908, Kammerlingh-Onnes experiments on liquid He(a GPa. A 10% drop in resistivity perconductivity at around 1.5 K. Hg resistance: 0.08 ohm 5K to 0.000003 ohm @ 4.2K Shimizuet al Nature 2001. 112316 The temperature dependence of the magnetization 986, G. Bednorz, K. H Muller (BM,. La-Ba-Cu-O Oxide: Te=35K expanded in the upr K. The lower inset shows the disappearance of the Meissner signal in iron when the pressure is decreased to 3.5 GPain the b c.c. phase. in La.0(1986tp Discovery of Superconduct Brief History of Superconductivity b1911 Kamerlingh Onnes discovered superconductivity in Hg b1913 Kamerlingh Onnes won the Nobel Prize in Physics 21953 Superconductivity was reported in V Si at Tc=175K 21972 Bardee, Cooper& Schrieffer won the Nobel Prize 86 Muller and Bednorz (IBM-Zzurich) 21987 Muller and Bednorz won the Nobe forefront of research 1988 Te was pushed to 120K in a ceramic containing Ca and a1993 Hg Ca Cu, Og was found to superconduct at Te=133K 39K Superconductivity in MgB2 Characteristics of Superconductors In MgB, hexa Ing or uI until a force is appley rs., ring continues in centered on the hexagons duced magnetic field ure2001,410,63 exactly opposes the applied field. The material is strongly MgB, like graphite, has strong o bonds in the carbon atoms, not all the a the boron planes has a much stronger effec ate a magnet above the of strong electro surface of the superconductor
3 Superconductivity of Iron (Fe) Shimizu et al., Nature 2001, 412, 316 •Temperature dependence of the electrical resistivity of iron at 25 GPa. A 10% drop in resistivity indicates the onset of superconductivity at around 1.5 K. The temperature dependence of the magnetization of iron under pressure obtained by cooling the sample at a magnetic field of 130 G. The signal at 21 GPa (the area enclosed by the dotted line is expanded in the upper inset) shows the appearance of diamagnetism at temperatures below 1.7 K, which is confirmed by the signal given by tin at 2.7 K. The lower inset shows the disappearance of the Meissner signal in iron when the pressure is decreased to 3.5 GPa in the b.c.c. phase. 1908, Kammerlingh-Onnes experiments on liquid He ( a few ml) Hg resistance: 0.08 ohm @ 5K to 0.000003 ohm @ 4.2 K 1986, J. G. Bednorz , K. H. Muller (IBM) La-Ba-Cu-O Oxide: Tc = 35 K Superconductivity Discovery of Superconductivity in La-Ba-Cu-O (1986) “At the extreme forefront of research in superconductivity is the empirical search for new materials.”(1983) Brief History of Superconductivity 1911 Kamerlingh Onnes discovered superconductivity in Hg at Tc=4K 1913 Kamerlingh Onnes won the Nobel Prize in Physics 1933 Meissner and Ochsenfeld discovered the Meissner Effect 1941 Superconductivity was reported in Nb nitride at Tc=16K 1953 Superconductivity was reported in V3Si at Tc=17.5K 1962 Development of first superconducting wire 1972 Bardee, Cooper & Schrieffer won the Nobel Prize in Physics 1986 Müller and Bednorz (IBM-Zurich) discovered High Temperature Superconductivity in La-Ba-Cu-O at Tc=35K ! 1987 Müller and Bednorz won the Nobel Prize in Physics 1987 Superconductivity was found in YBCO copper oxide at Tc=92K !!! 1988 Tcwas pushed to 120K in a ceramic containing Ca and Tl 1993 HgBa2Ca2Cu3O8 was found to superconduct at Tc=133K 39K Superconductivity in MgB2 In MgB2 , hexagonal honeycomb layers of boron atoms alternate with layers of magnesium atoms, centered on the hexagons. MgB2 , like graphite, has strong s bonds in the planes and weak p bonds between them, but since boron atoms have fewer electrons than carbon atoms, not all the s bonds in the boron planes are occupied. And because not all the s bonds are filled, lattice vibration in the boron planes has a much stronger effect, resulting in the formation of strong electron pairs confined to the planes. Nagamatsu et al. Nature 2001, 410, 63 Characteristics of Superconductors Loss of Resistance! ¾¾ Zero electrical resistivity. This means that an electrical current in a superconducting ring continues indefinitely (at least for a very long time ~ years … ), without dissipation through the ring or until a force is applied to oppose the current. MeissnerEffect! ¾¾ Superconductors expel all magnetic flux in a process called the Meissner effect. The magnetic field inside a bulk sample is zero. When a magnetic field is applied, current flows in the outer skin of the material, leading to an induced magnetic field that exactly opposes the applied field. The material is strongly diamagnetic as a result. A superconductor excludes magnetic flux. In this experiment, this is used to levitate a magnet above the surface of the superconductor
Meissner Effect Two Easy Experiments Showing Meissner Effect CWhen a superconducting sample is cooled below the magnetic field (ie. lines of the induction b)are quid nitrogen is added to a reservoir beneath the superconductor. (The ushed out peroonductor is actually just out of of the cup )A maller magnet levitates about a A superconductor is a perfect diamagnet! centimeter above it B Three Barriers of Superconducting Materials Critical Magnetic Field wA sufficiently strong external magnetic field can destroy the superconducting state 素 Jc High Tc(critical temperature) ohase diagram of I experimental High Je (critical current density) Application Uses of Superconductors [Levitation wire MagLev trains have been under development in Japan for the past two decades rgy loss by ahe train floats above the track using superconducting High voltage needed Wire with superconduct magnet dThere's no friction between the train and the"rail so les E Wire with superconductor energy is lost and the train can reach much higher speeds No energy loss No high voltage needed. 戀 Storage of electricity. Cut end of superconductor
4 Meissner Effect When a superconducting sample is cooled below Tc in the presence of an external magnetic field, the magnetic field (i.e., lines of the induction B) are pushed out. A superconductor is a perfect diamagnet ! Two Easy Experiments Showing Meissner Effect Liquid nitrogen is added to a reservoir beneath the superconductor. (The superconductor is actually just out of sight beneath the rim of the cup.) A smaller magnet levitates about a centimeter above it. Three Barriers of Superconducting Materials High Tc (critical temperature) High Hc (critical magnetic field) High Jc (critical current density) Critical Magnetic Field A sufficiently strong external magnetic field can destroy the superconducting state critical magnetic field phase diagram of Itype superconductor experimental data Application wire Existing wire - Energy loss by resistance - High voltage needed Wire with superconductor - No energy loss - No high voltage needed. - Storage of electricity. Cut end of superconductor wire Wire with superconductor Uses of Superconductors [Levitation] “MagLev”trains have been under development in Japan for the past two decades The train floats above the track using superconducting magnets. There’s no friction between the train and the “rail”so less energy is lost and the train can reach much higher speeds
Application Magnetic levitating Vehicle Josephson devic principle SQUID Superconducting QUantum Interference Device train conducting loop interrupted in 2 places by sephson junctions When sufficient electrical current is conducte proportional to the strength of any nearby magnetic field. car with superconductor? Uses of Superconductors Application IMagnetic Resor per computer doctors to see what is happening inside the body without Without superconductor I directly performing surgery large heat, large electric power eld of mRI as the superconducting magnet can be smaller and more efficient than an equivalent conventional magnet. no heat, small electric power use Application-Particle Colliders Hi gh Temperature Superconductors Particle colliders are v running tracks that are cUprate superconductors have been the focus of researcher because they conduct at relatively high temperature e ight before they are collided with one angotherspeed of The collision usually nough energy to split Particle colliders were used to discover many sub They do this by cycling the particle using magnetic fields, continually inereasing the speed of the particle tn the Y, B, Cu, O compounds: Y, Ba, and O have xidation states of +3, +2, and-2, respectively. tThis results in copper having mixed oxidation states +2 a similar result is obtained for the other materials tTheir structures are related to that of perovskite(CaTiO
5 Application Magnetic levitating Vehicle •principle •car with superconductor? •train Application Josephson device SQUID (Superconducting QUantum Interference Device ) A superconducting loop interrupted in 2 places by Josephson junctions. When sufficient electrical current is conducted across the squid body, a voltage is generated proportional to the strength of any nearby magnetic field. Uses of Superconductors [Magnetic Resonance Imaging] MRI is a technique developed in the 1940s that allows doctors to see what is happening inside the body without directly performing surgery. The development of superconductors has improved the field of MRI as the superconducting magnet can be smaller and more efficient than an equivalent conventional magnet. Application Super computer - Without superconductor : large heat, large electric power use - with superconductor : no heat, small electric power use ß Particle colliders are very large running tracks that are used to accelerate particles (i.e. electrons, positrons, hadrons and more) to speeds approaching the speed of light before they are collided with one another. –The collision usually possess enough energy to split the particles into smaller particles. –Particle colliders were used to discover many sub - nuclear particles such as taus and neutrinos. ß They do this by cycling the particle using magnetic fields, continually increasing the speed of the particle. Application ¾ Particle Colliders High Temperature Superconductors Cuprate superconductors have been the focus of researchers because they conduct at relatively high temperature (Tc > 77K). In the Y, Ba, Cu, O compounds: Y, Ba, and O have oxidation states of +3, +2, and -2, respectively. This results in copper having mixed oxidation states +2 and +3. A similar result is obtained for the other materials. Their structures are related to that of perovskite (CaTiO3 ). Compound Tc/K Compound Tc/K YBa2Cu 3O7 93 Tl 2CaBa2Cu 2O8 119 YBa2Cu 4O8 80 Tl 2Ca2 Ba2Cu 2O7 128 Y2 Ba4Cu 7O15 93 TlCaBa2 Cu2 O7 103 Bi2 CaSr2 Cu2O6 92 TlCa2B a2Cu 3O8 110 Bi2 Ca2S r2Cu3 O10 110 Tl 0.5Pb0.5Ca2S r2Cu 3O9 120
Perovskite structure Rocksalt structure and Fluorite Structure Rocksalt Structure Fluorite Structure erovskite structure coordinationofTi The Perovskite(CaTiO.Unit Cell Perovskite R: ionic radius: R(O*)=1.40A tructure:ABO aa and ag natural size of each layer If a polyhedron is used to represent the Ti centered coordination environments, then anO atom lies at each vertex. the Ca= is shown in black. R(A)+R(O=aa R(B)+R(O)=a,/2 tolerance factor: O. 90- An 0 atom lies at a s shown in blac B10 Tolerance Factor 1 R(A)+R(O)a Structure of Cuprate Superconductors √2RB)+RO 1Oxygen' s from a CuO, layer are"shared by the perovskite unit cell. The actual cell size a is determined from aa and a t a I is needed. Layered perovskites are more Hn the perovskite cell, the Ba *(Black) and Ya+ bstitute for Ca2+. The Cu(blue) tolerant centers substitute for Ti(v) a=3.8~4.0A R(A)=1.3~1.4A,R(B)=0.5~06A Three factors to consider 1. valence 2. oxygen coordination number 3. ionic radius
6 Perovskite Structure Octahedronal coordination of Ti Perovskite Structure Rocksalt Structure and Fluorite Structure Rocksalt Structure Fluorite Structure The Perovskite (CaTiO3 ) Unit Cell If a polyhedron is used to represent the Ti centered coordination environments, then an O atom lies at each vertex, the Ca 2+ is shown in black. An O atom lies at each vertex, the Ca 2+ is shown in black. Perovskite structure: ABO3 B A a a R(B) R(O) R(A) R(O) 2 1 t = + + = × tolerance factor: R: ionic radius: R(O 2- ) ≡ 1.40 Å aA and aB: natural size of each layer AO layer: R( A) + R(O) = a A / 2 R(B) + R(O) = aB / 2 BO2 layer: B O O A The actual cell size a is determined from aA and aB . t ≈ 1 is needed. Layered perovskites are more tolerant. a = 3.8 ~ 4.0 Å R(A) = 1.3 ~ 1.4 Å, R(B) = 0.5 ~ 0.6 Å Three factors to consider: 1. valence 2. oxygen coordination number 3. ionic radius Tolerance Factor: B A a a R(B) R(O) R(A) R(O) 2 1 t = + + = × Structure of Cuprate Superconductors Oxygen's from a CuO2 layer are “shared”by the perovskite unit cell. In the perovskite cell, the Ba2+ (Black) and Y3+ (Gray) ions substitute for Ca2+. The Cu (blue) centers substitute for Ti(IV)
Structure of Cuprate Superconductors Cuprate Supero conductors . The Cuprate superconduct . The CuO, layers are responsible for the lI contain a layer with superconducting properties "The other layers serve as sources of electrons -This layer can be planer .The copper 3d and oxygen 2p atomic orbitals perature for significant orbital cuprate superconductors have mixing>band structure. layer structures as well This band is half filled because Cu(n) has a d9 -For example configuration TI2 Ca, Ba CugO . The half-filled band is tuned electronically by the effects of the neighboring layers in the lattice T, vs Number of CuO, Layers Why Do They Superconduct? T株,C In compounds such as Y Ba Cu, O- the metal ion ( i.e But an individual metal ion cannot be partially oxidized. There will be holes'of positive charge(Cu+ ions)within the lattice This type of superconductor is referred to as a p-type Compounds can also be de to insert extra electrons into the lattice (i. e. a reduction), e. g. La, cuOa+ -This is called an n-type superconductor. Why Do They Superconduct? Lanthanum Barium- Copper Oxi One explanation involves the use of holes within the Superconductor electrons travel along the ion planes in the lattic oThis ceramic material As an electron passes a positive hole(due to oxidized cation. was the first of a ner Liy.a, CaOt class of high temperature ductors. It is made by randomly -This is due to electrostatic repulsion. substituting so The oxidized cation(Cu+)then reduces, and the reduced o t le.ps on(Cu+)oxidizes lattice of lanthanum -Effectively, the hole moves backwards (as an electron copperoxide in what is moves forward This“ extra nt that is caused by the normal current is the super
7 ßThe Cuprate superconductors all contain a layer with stoichiometry CuO2 . –This layer can be planer ßThe other high-temperature cuprate superconductors have layer structures as well. –For example: Tl2Ca2Ba2Cu3O10 Structure of Cuprate Superconductors Cuprate Superconductors ßThe CuO2 layers are responsible for the superconducting properties. ßThe other layers serve as sources of electrons. ßThe copper 3d and oxygen 2p atomic orbitals are close enough to allow for significant orbital mixing ‡ band structure. –This band is half filled because Cu(II) has a d9 configuration ßThe half-filled band is tuned electronically by the effects of the neighboring layers in the lattice. Tc vs Number of CuO2 Layers Why Do They Superconduct? ßIn compounds such as YBa 2Cu3O7-x the metal ion (i.e. copper) is partially oxidized. ßBut an individual metal ion cannot be ‘partially’oxidized. –Instead, the lattice will be comprised of a ratio of Cu2+ to Cu3+ ions, depending on x. –There will be ‘holes' of positive charge (Cu3+ ions) within the lattice. –This type of superconductor is referred to as a p-type superconductor ßCompounds can also be doped to insert extra electrons into the lattice (i.e. a reduction), e.g. La2CuO4+x –This is called an n-type superconductor. Why Do They Superconduct? One explanation involves the use of holes within the superconductor. ßWhen a current is applied to the superconductor, the electrons travel along the ion planes in the lattice. ßAs an electron passes a positive hole (due to oxidized cation, Cu3+) in a neighboring plane, it will push negative charge from orbitals on a reduced cation (such as Cu2+) towards the hole. –This is due to electrostatic repulsion. ßThe oxidized cation (Cu3+) then reduces, and the reduced ion (Cu2+) oxidizes –Effectively, the hole moves backwards (as an electron moves forwards). –This “extra”current that is caused by the normal current is the supercurrent. Lanthanum-Barium-Copper Oxide Superconductor This ceramic material was the first of a new class of high temperature superconductors. It is made by randomly substituting some barium atoms into the lattice of lanthanumcopper-oxide in what is termed a solid solution
Yttrium. Barium- Copper Oxide Superconductors eThis ceramic YBa Cu,O-6 Ba material was the first of the high (YBa yCu perconductors to Oxygen Deficient ange at a Triple Perovskite temperature above the liquid nitrogen absent oxyge temperature (77 K Properties 8 value YBa. CugO, superconductor YBa CugO7-8 at temperature T. As 8 1)T decreases YBayCugOs semiconductor oxygen lost from base of from orthorhombic to unit cell tetragonal rearrange in base T= tetragonal Changing Properties? Oxides Superconductors Perovskite structure Can substitute many elements into YBa2Cu3O7 tructure BAlun Y→ lanthanides· no change in T ●Ym Y=other elements'decrease in Te Ba→Sr,Ca· decrease in t Cu= transition metals. decrease in T Cu→Au· very slight increase? Ba→La· very slight increase? Generally detrimental rIght: Removal of 2/9 of oxy gens gives defect perovskite structure, O-s(xd0.2)"123 Superconductor C N Ba= 10, C.N. Y=8
8 Yttrium-Barium-Copper Oxide This ceramic material was the first of the high temperature superconductors to make the phase change at a temperature above the liquid nitrogen temperature (77 K). Superconductors YBa2Cu3O7-d Perovskite? (YBa2 )Cu3O9-x Oxygen Deficient Triple Perovskite Crosses mark absent oxygen Properties YBa2Cu3O7 superconductor - resistance lost completely at temperature Tc YBa2Cu3O6 semiconductor - oxygen lost from base of unit cell YBa2Cu3O7-d As d increases: 1) Tc decreases 2) symmetry changes from orthorhombic to tetragonal (oxygen atoms rearrange in base) O = orthorhombic T = tetragonal d value Changing Properties? Can substitute many elements into YBa2Cu3O7 structure: Y Þ lanthanides - no change in Tc Y Þ other elements - decrease in Tc Ba Þ Sr, Ca - decrease in Tc Cu Þ transition metals - decrease in Tc Cu Þ Au - very slight increase? Ba Þ La - very slight increase? Generally detrimental! Oxides Superconductors vs Perovskite Structure Left: 3perovskite unit cells, CaTiO3 × 3 = Ca3Ti3O9 Center: Replace Ca with Ba, Y; Replace Ti with Cu® YBa2Cu3O9 orthorhombic unit cell count Right: Removal of 2/9 of oxygens gives defect perovskite structure, YBa2Cu3O7 -d (x»0.2) “123”Superconductor C.N. Ba = 10, C.N. Y = 8
YBa,Cu,O- as a defective perovskite Two types of Cu site pyramids Chains of vertex-linked Cuo, squares hese are indicated in a Polyhedral Representation Cuo2 KNiFa Structure (La, Sr) CuO(T Phase) KaNiF,is a derivative with deri structure of perovskite 9 structure. This structure the alternate stacking 0000 can be regarded as the o alternate stacking of 2D perovskite structure perovskite layer and aver and rocksalt tructure unit along c Ba Laz+v is K,NiF, structure, Tc(O)=g ↓ The same structure Cu with the first cupper F structure and its (110) projection La, Ba CuO (T 35K) Alternative Views of the La Cuo, Structure Alternative Views of the La Cuo Structure +Doped La, CuO, CuO, are the first HighT structure as based on SuperconductingOxide r 1. Sheets of elongated for which bednorz CuO. octahedra Miller Nobel Prize 2. Layered networks 中aCuO, may be viewed a t of Cu0 6, connected ABAB. arrangement of only by Last ions known as an AB Perovskite
9 YBa2Cu3O7 as a Defective Perovskite Two types of Cu site Layers of CuO5 square pyramids Chains of vertex-linked CuO4 squares These are indicated in a Polyhedral Representation CuO2 BaO CuO BaO CuO2 Y CuO2 K2NiF4 Structure K2NiF4 structure and its (110) projection K2NiF4 is a derivative structure of perovskite structure. This structure can be regarded as the alternate stacking of 2D perovskite layer and Rocksalt Layer. BaxLa2-xCuO4-y is K2NiF4 structure，Tc(0)=38K (La,Sr)2CuO4 (T Phase) A superconductor with Derivative structure of K2NiF4 Can be regarded as the alternate stacking of perovskite structure unit containing Cu-O layer and rocksalt structure unit along c axis. The same structure with the first cupper oxide superconductors La2-xBaxCuO4 (Tc=35K). Doped La2CuO4 {La2-xSrxCuO4 and La2-xBaxCuO4 } are the first (1986) High-Tc Superconducting Oxide (Tc ~ 40 K) for which Bednorz & Müller were awarded a Nobel Prize La2CuO4 may be viewed as if constructed from an ABAB... arrangement of perovskite cells - known as an AB Perovskite! Alternative Views of the La2CuO4 Structure Alternative Views of the La2CuO4 Structure We may view the structure as based on: 1.Sheets of elongated CuO6 octahedra, sharing only vertices 2.Layered networks of CuO4 6- , connected only by La3+ ions
(Nd, Sr)2(Nd, Ce)2 Cu2O&(T* Phase (Nd, Ce)2 CuO(T' Phase) DErivated from K NiF lose one vertex and thus forr lose two vertexes and thus Nd, Sr), (Nd, Ce),Cu,O be regarded as the altemate form CuO, plan HNd ce)CuO, can be layer and rocksalt layer alor fluorite structure unit along C axIs STe28K Cd NE c axis. STe=24K TIBa2 Ca, Cu, O2n+3 Supercon uctors Pb, Sr2- La Cu,O (Pb2202) *Can be regarded as special w with singer gle TIO layer ee Te is 50K, 103K and e8> om La CuO4, in which one CuOe 117K, respectively OoOoO Po form liner coordination structure hey are built up by two kinds of clone Rocksalt layers and in octahedron coordination S, Lao structure (+2 valence)and the Perovskite lavers Comparison of Pb2202 and La CuOA La CaCu,O6 sThis structure contains two 488能m ②的 face-to-face CuO square pyramid Ouo lavers. It esult of two-fold ygen-deficient perovskite 000Oo ONO L structure from two layers of Cuo CO octahedron losing the common eee C vertex oxygture can also be CaAt (Sr, La)o (La, St)0 A9 ON 5. ws hiph abed by glwp eaves ate geer Pb, (Sr, La),Cu, Oe (La, Sr), CuO e eee ca deficient perovskite. (T phase)
10 (Nd,Sr)2 (Nd,Ce)2Cu2O8 (T* Phase) Derivated from K2NiF4 structure. CuO6 octahedron lose one vertex and thus form CuO5 square pyramids. (Nd,Sr)2 (Nd,Ce)2Cu2O8 can be regarded as the alternate stacking of CuO5 square pyramids layers, fluorite layer and rocksalt layer along c axis. Tc=28K (Nd,Ce)2CuO4 (T’Phase) Derivated from K2NiF4 structure. CuO6 octahedron lose two vertexes and thus form CuO4 plane. (Nd,Ce)2CuO4 can be regarded as the alternate stacking of CuO4 plane and fluorite structure unit along c axis. Tc=24K TlBa2Can-1CunO2n+3 Superconductors TlBa2Can-1CunO2n+3 (n=1,2,3… ) series with single TlO layer, Tc is 50K，103K and 117K，respectively. They are built up by Rocksalt layers and oxygen-deficient Perovskite layers. Ba Pb2Sr2-xLaxCu2O6 (Pb2202) Can be regarded as special K2NiF4 structure, and derivated from La2CuO4 ,in which one CuO6 octahedron loss all oxygens and form liner coordination structure. There are two kinds of Cu,one in octahedron coordination structure (+2 valence)and the other in linear coordination structure (+1 valence). Tc=32K Comparison of Pb2202 and La2CuO4 Pb2 (Sr,La)2Cu2O6 (La,Sr)2CuO4 (T phase) La2CaCu2O6 This structure contains two face-to-face CuO5 square pyramid layers. It is a result of two-fold oxygen-deficient perovskite structure from two layers of CuO6 octahedron losing the common vertex oxygen. This structure can also be regarded as the derivative in which the single perovskite layer is replaced by two layers oxygendeficient perovskite