11 Renato F. Jardim Instituto de Física Universidade de São Paulo Brazil Novos Óxidos Metálicos com Propriedades Eletrônicas Interessantes Maringá, Setembro de 2011

22 Introduction Motivation Examples of Interesting Families of Oxides Crystal Structure and General Physical Features Electronic Properties Metal-Insulator Transition - Nickelates Colossal Magnetoresistance – Manganites Few Applications Superconductivity – Cuprates Preliminary Conclusions Outline

33 Motivation 1)Efficient, Stable, Tunable, and Easy to Synthesize (including thin films) ! 2)Cheap (Methods and Materials) and Bringing New Physics in Materials Science ! 3)Easy for Modelling and Computing ! Oxides They are Abundant in the Nature !

4 Manganites - La 1-x Ca x MnO 3 La Ca Mn Mn O 3 2- Examples of Interesting Families of Oxides A = La, Y, Pr, Bi etc A’= Ca, Sr, Ba etc B = 3d (Transition Metal) and their solid solutions !!! Perovskites A 1-x A’ x BO 3

55 Tabela Periódica Alcalino Metal 3d Terra Rara O, Cl, F General Formula A 1-x A’ x BO 3

66 Examples of Interesting Families of Oxides Perovskites General Formula A 1-x A’ x BO 3 Tailoring Materials 1) Periodic Table 2) Materials Science 3) Phase Diagram 4) Thermodynamics – Phase Transitions 5) Magnetoelectric Coupling – Multiferroic Behavior 6) Strong Correlation Systems 7) Charge and Orbital Ordering

77 Alterando as Propriedades do Sistema Exemplo : Substituir Parcialmente La +3 por Ca +2 Produção de Pares Mn +3 /Mn +4 Criação de Buracos (Holes) Uma Série de Novas Fases com Diferentes Propriedades Magnéticas e de Transporte Examples of Interesting Families of Oxides LaMnO 3

8 Diagrama de Fase La 1-x Ca x MnO 3 Variação do teor de Ca ou de buracos (holes) ! Metal Isolante Examples of Interesting Families of Oxides LaMnO 3 CaMnO 3 Paramagnetico ???

99 Crystal Structure and General Physical Features Facil de modelar – Primeiros Princípios Física é concentrada nos octaedros de (TM)O 6 Portadores são Fortemente Correlacionados (a Física é alterada (e muito !))

10 Interação de Dupla Troca Interação de dupla troca - Double Exchange Interaction - Pares Mn +3 /Mn +4 Elétrons e g podem ser Itinerantes - Criação de vacâncias eletrônicas (holes) via Mn +4 egeg t 2g Mn +3 Mn +4 Elétrons t 2g são menos hibridizados com estados 2p e estabilizados pelo campo cristalino ! Localizados pelas fortes correlações eletrônicas e apresentam S = 3/2 ! Elétron e g são Itinerantes Análogo aos Elétrons de Condução ! t ij Electronic Properties

11 Transição Ferromagnética T C Transição metal-isolante T MI Forte correlação entre T MI e T C Ferromagnético Metálico Antiferromagnético Isolante Paramagnético Isolante Resistividade Elétrica e Magnetização em Manganitas La 0.6 Y 0.1 Ca 0.3 MnO 3 Electronic Properties

12 Acoplamento dos Graus de Liberdade de Spin, Carga e Rede Electronic Properties Variando parâmetros termodinâmicos La 0.7 Ca 0.3 MnO 3

13 Magnetorresistência Colossal La 0.6 Y 0.1 Ca 0.3 MnO 3 Electronic Properties Applying a Magnetic Field Sensor !!!

14 Electronic Properties Metal-Insulator Transition (Nd 1-x Eu x NiO 3 ) - First order nature of the transition; - Thermal Hysteresis - Tuning of T MI Perovskites Isolante Metal Variando a Temperatura

15 Electronic Properties Applying Pressure La 0.7 Ca 0.3 MnO 3 Sensor !!!

16 Electronic Properties Sensor !!! Nd 1-x Eu x NiO 3 Applying Pressure dT MI /dP quite high and close to 300 K!

17 Electronic Properties Parâmetro não Termodinâmico – Corrente Elétrica Cr-doped Nd 0.5 Ca 0.5 MnO 3 Sensor !!!

18 Aplicação Tecnológica LaNiO 3 -  Cu ~ 3x10 -6  300 K - Comportamento Metálico - Estrutura Perovskita (Casamento de Rede) - Fácil Preparação Filmes Finos de LaNiO 3 Dip Coating Vamos ver isso !

19 +  + Complexo M-CA Etileno Glicol Polímero H 2 O Preparação de amostras – Resumo Didático Método dos Precursores Poliméricos M n+ Ácido Cítrico - AC complexo M-CA Metal Tratar Termicamente – Filmes Finos Aplicação Tecnológica

20 Aplicação TecnológicaRevista FAPESP Material com constante dielétrica da ordem de 2000 (Aplicação para Memória Ferroelétrica). Utilizar filmes finos de LaNiO 3 como eletrodo ao invés de Si-Pt em dispositivos.

21 Electronic Properties Superconductivity (Bi,Pb) 2 Sr 2 Ca 2 Cu 3 Oy - Supercondutividade nos planos de CuO - Forte Anisotropia - T C ~ 110 K Componentes Intergranulares ! Limitam a Aplicação Tecnológica ! Intergrain Properties of (Bi,Pb)-2223 Vamos Avançar Nesse Tópico ! Comportamento Metálico – Resistência de Superfície – Aplicação !

22 Caso Extremo – Separação Intra & Intergranular Sm 1.8 Ce 0.2 CuO 4-y Efeitos de Granularidade !!! (Restrições para Aplicações Tecnológicas !)

23 Efeitos de Granularidade (Simple Picture) !!! Como Melhorar Isso ? Vamos Avançar no Tópico !

24 Introduction Motivation Grain Boundary Angle Dependence on J c (0) Overcoming the misorientation of the grains in tapes and powders (Bi,Pb)-2223 and its properties Intergrain Properties of (Bi,Pb)-2223 Experimental Procedure - Sample preparation and characterizations Experimental Results X-ray diffraction, SEM,  (T,B a ) – Uniaxial and hydrostatic pressures Magnetization M(T,B a ) Three-level superconducting system Correlating normal and superconducting properties Transport Barkhausen-like noise Preliminary Conclusions Outline

25 Introduction - Motivation ● Grain Boundaries (GB) Limit Current Pathways in Polycrystalline Samples and Tapes ● Microcracks ● Misalignment of the Neighboring Grains – Angle  ● Increasing  results in a decrease of the spacing between the GB dislocations  : for  0 > 2 – 6 º ►  ~  ► J c (0) decreases ● Low vs. High Angles – Experimental Results J c (0) ~ exp(-  /  0 ) ● Deviation by > 2-3 º would already reduce J c (0) significantly !!! c-axis

26 H = 0 J c (0) ~ exp(-  /  0 ) R. Held et al., PRB (2009) For H > H c1 Transition from Abrikosov (A) – Josephson (J) Vortices Grain Boundary Angle Dependence of J c (0) For  «  0 Vortices on GB Abrikosov Vortices Normal Cores l(  ) Pinned by GB Increasing  ► increases l(  ) Mixed AJ Vortices Gurevich et al. PRL (2002)

27 Routes for the Alignment of the Grains ▼ Mechanical Deformations (rolling process, lamination, stretching etc) Controlling the Microstructure (T, atmosphere etc) Addictives during the Synthesis (composite + pinning) Hot Pressing Cold Pressing The TASK is ► To Align the Grains c-axis Electrical Current Examples for Practical Applications

28 YBCO Coated Tape – Close up Outer Cu strips can be replaced by stainless steel strips J c (77 K, 0) ~ 10 2 – 1.5x10 2 A/cm 2 width 4mm, thickness 0.1 – 0.2 mm, length 0.1 km Oriented buffer layer avoiding chemical reaction

29 (Bi,Pb)-2223-Ag Tape – Close up J c (77 K, 0) ~ 10 2 – 2x10 2 A/cm 2 width 4mm, thickness 2 mm, length 1 km ● Kyushu Institute of Technology, Japan (2010) Superconducting Magnet 77 K; 50 A; generating 0.5 T Dimensions: 132 mm outside  ; 52 mm inside  ; 120 mm in height Weight is 3.5 kg.

30 The Bi-2223 (or (Bi,Pb)-2223) Material T c (onset) ~ 112 K T c (  = 0) ~ 105 K c ~ 37.1 Å a ~ b = 5.4 Å ● Tetragonal crystal structure – Space Group P222 ● Two charge-reservoir layers (Bi(Pb)-O, Sr-O) sandwiching three CuO 2 planes ● T C is little sensitive to the Oxygen content ● No evidence of ageing effect ● Anisotropy  (~ 30 ???) is lower than Bi-2212 ● H c1 (77 K) ~ 10 mT (100 Oe) » YBCO (~ 40 Oe) Critical Current Density

31 ● J c (77 K, 0 T) ~ 70x10 3 A/cm 2 - filaments (1999) ● J c (77 K, 0 T) ~ 15x10 3 A/cm km long (  ~ 1 mm 2) (2002) ● Local J c (77 K, 0 T) up to 1.8x10 5 A/cm 2 - (2001) ● J c (77 K) of the grains ~ 5x10 8 A/cm 2 - (2001) ● 19-filament tape – Local J c (77 K, 0 T) ~ 2x10 5 A/cm 2 ; tape monocore ~ J c (77 K, 0 T) ~ 4x10 4 A/cm 2 (2009) ● Commercially available current leads (~ 1m long) J c (77 K, 0 T) ~ 2x10 3 A/cm 2 ● J c (77 K) of the grains ~ 5x10 8 A/cm 2 - (2001) ~ to the limit of J c !!! Problem of the softness of the Ag matrix (Tapes) by applying dispersed MgO in the Ag matrix Solved by adding a thin layer of stainless steel reinforcement to both sides of the tapes enabling the tapes to withstand a tensile stress of 300 MPa and a tensile strain of 0.5% at 77 K (Bi,Pb)-2223 – Critical Current Density in Tapes & Filaments

32 Intergrain Properties of (Bi,Pb)-2223 ● Much has been learned about the intragranular properties but little about the intergranular properties of High-T c ● Intergranular properties are very important for understanding the tunneling of the carriers between adjacent grains; ● very high B (B < 14 T) are well studied ● How about the transport very low B (B < 70 mT) ? ● The very low magnetic fields are essentially absent !!! ● Very high T C, relatively easy to be synthesized, ● Sample Preparation – Bi 1.65 Pb 0.35 Sr 2 Ca 2 Cu 3 O 10+  ● XRD and SEM ● Magnetization M(T, B) ● Transport very low B (B < 70 mT) ● Transport very high B (B < 18 T) ● Transport Barkhausen-like B < H c1 Experimental

33 Sample Preparation and Physical Characterizations Few Important Steps for Single-Phase Powder Material Powder Preparation – Mixing BaCO 3 ; SrCO 3 ; CuO; Bi 2 O 3 ; PbO Heat Treatments 750 ºC ( ºC ( ºC (40h + 40h + 40 h) Uniaxial (100 – 600 MPa);  ~ 10 mm; thickness < 1 mm Cold Pressed Isostatic (100 – 300 MPa);  ~ 10 mm; thickness < 1 mm Last Heat 850 ºC (40 h) – After Pressuring !!! Summary of the Pressuring Process

34 Summary of the Process Problems in Compacting Powders Uniaxially End Capping (high die-wall friction) Ring Capping (excessive differential Springback) Lamination (excessively high P) Vertical Cracks (springback) Schematic Draw - Pressings Expected Results

35 Highly oriented grains along the c direction Top View XRD Data That’s what we want !!! (but it is not easy to get it !)

36 XRD Powder Diffraction Data taken mostly on pellets ! Powder Sample BP5 BP4 BP3 BP2 Lotgering factor F(00l)

37 Lotgering factor F(00l) ● I 0(00l) and I 0(hkl) are the intensities of (00l) and (hkl) peaks (powder sample) ● I (00l) and I (hkl) are the intensities of (00l) and (hkl) peaks (pellet sample) Increasing Uniaxial Compacting Pressure ▼ Better alignment of the grains along the c-axis !!! Comparing Uniaxial & Hydrostatic Pressures Govea-Alcaide et al. (2007)

38 Comparing Uniaxial and Hydrostatic Pressures Mune et al. (2007) J c (77 K, B a ); B a < 7 mT (70 Oe) Uniaxial Isostatic J c (77 K, 0) is much higher for the uniaxially compacting sample ! The pressure is not homogeneous throughout the sample Josephson-like

39 SEM Images Inhomogeneous distribution of pressure face A face B ● Relative intensity of the peaks ● (200) 25 % face A; 50 % face B ●  (T, H) data face A face B B a = 43 mT B a = 0 mT T off Changes are related to: ● ≠ degree of texture ● Intergrain connectivity

40 Grain Size l ~ 4  m thickness d ~ 0.1  m SEM Images ● Bi-2212 – Pressed ~ 490 MPa ● Smaller grains ● Low degree of orientation ● (Bi-Pb)-2223 (~ 590 MPa) ● Platelet-like Grains ● Highly Oriented Grains The superconducting properties

41 Temperature and magnetic field dependence of magnetization M(T) The Model (i) Grains behave as a Bean-like superconductor (in the window of T and B a ); (ii) Grains exhibit saturation at the same applied H s ; (iii) The M(B a ) curves deviate from the linear behavior at similar values of B cl – Determine H c1g. H c1g HsHs

42 Three-level superconductivity system Critical Current Data + Virgin curves + Returning curves B max + ????Flux-trapping curves Dois “Plateaus”

43 Three-level superconducting system ● the superconducting grains; ● the superconducting clusters (strong coupled superconducting grains); ● weak links between superconducting clusters. grains clusters weak links between clusters From M(77 K, H) data J cg ~ 1x10 8 A/m 2 Slightly smaller J cg ~ 5x10 8 A/m 2 Flückiger (2009)

44 Correlation between normal and superconducting properties Set of samples (Bi-Pb)-2223 P T con ~ constant; T off (table) Same Grains ≠ intergranular features

45 Temperature dependence of the electrical resistivity -  (T) Let`s borrow a model (Diaz et al. (PRB 1997))  n has two contributions (i)Misalignment of the grains (ii) Microstructural defects X-crystals (T. Fuji) Paracoherent state  ab = 0

46 Paracoherent state - electrical resistivity -  (T) This is a complicated measurement (Joule-self heating effect, temperaure controll etc) Grains are in the superconducting state ! Current density sufficient to overcome the intergranular one !

47 Parameters of the samples subjected to uniaxial pressure Appreciable reduction (  str ) of microstructural defects ! Increasing of the degree of texture (f) ! “Perfect” polycrystalline sample (no voids, cracks, extra phases etc)  str = 1, f ≈ 1/3 ! J c (77 K, 0 T) ~ 4x10 2 A/cm 2 - our sample J c (77 K, 0 T) ~ 2x10 3 A/cm 2 - commercial

48 Intergranular Critical Current and Pinning Energy Flux-Trapping curves The behavior of J c (77 K, B a ) can not be fully described by the Bean model Three-level superconducting system ! JcJc BaBa Virgin Curves Josephson-like

49 Correlating Critical Current, Pinning Energy, and Defects ● J c (0) and U 0 scale with  n ● The behavior is related to changes in the microstructure (see Table) ● J c (0) changes little for P > 350 MPa: Is there any “limit” for Jc(0) ?

50 Transport Barkhausen-like noise in (Bi-Pb)-2223 Aim – To gain further information from the noise related to the movement of the “intergranular” vortices in (Bi-Pb)-2223 ● Noise is expected when an ac magnetic field penetrates the intergranular media; ● Analogous – Domain walls in ferromagnetic materials ● Here the noise is detected in  instead of M

51 Typical Barkhausen-noise data At 77 K H c1g > 7 mT Maximum B a ~ 5 mT ac triangular-wave Maximum Ba ~ 5.5 mT Frequency ~ 1 Hz  t = t f – t i t i – time where the noise first appears t f – time where the noise vanishes Sample is subjected to an excitation current [J/Jc(0) ~ 0.5]

52 Some Barkhausen-noise data J/J c (0) ● The noise occurs at ≠ “time” when the sample is subjected to ≠ J/J c (0)

53 ● The dissipation “process” is complicated ! very low B a (first stage) – vortex motion in few regions of the sample !!! Relevant issues to be addressed

54 Superconducting state Normal state Relevant issues to be addressed ● The dissipation “process” is complicated ! very low B a (first stage) – vortex motion in few regions of the sample !

55 Preliminary Conclusions ● General Issues ● Perovskites offer a unique opportunity for studying the wide range of physical properties in oxides; ● Their crystal structure is quite simple and can be modeled; ● Several physical features: metal-insulator transitions, magnetism, colossal magnetoresistance, ferroelectricity, multiferroic behavior and so on; ● Superconductivity ● Uniaxially pressed samples are a powerful tool for studying the intergranular features of High-T c materials; ● Issues of Interest: dissipation, current limited transport properties and so on; ● Excellent for disclosing the occurrence of a three-level superconducting system; ● Samples with high critical current density; ● Normal and superconducting parameters are easily correlated; ● Transport Barkhausen-like noise can be used for quality control (production of tapes and wires); ● Issues to be addressed: ● Material tailoring and nanotechnology (oxides); ● High quality singleX-tals; ● Theory: Strong correlated electron systems and quantum phase transitions.

56 Acknowledgements Marcia T. Escote – UFABC José A. Souza – UFABC Alessandro Carneiro – UFG Sueli Masunaga – USP Solange Andrade – USP Vagner Barbeta – FEI Maria J. Sandim – EEL Ernesto Govea–Alcaide – UO, Cuba Ivan Garcia Fornaris – UC, Cuba Pedro Mune – UO, Cuba Milton Torikachvili – SDSU, USA John Neumeier - MSU, USA Brazil Agencies

57 Um pouco do nosso Lab na USP - SP Bobina supercondutora ~ 17 Tesla Refrigerador de diluição T> 0,02 K Medidas de propriedades magnéticas Medidas de resistividade e susceptibilidade Bobinas supercondutoras ~ 20 Tesla Criostato de He 3 T > 0,4 K

58 Laboratório de Estado Sólido e Baixas Temperaturas Medidas de propriedades magnéticas (SQUID) Bobinas supercondutoras ~ 7 Tesla Temperatura 2K < T < 300K

59 Onde me encontrar………. OOPSSS !!!

60 Muito Obrigado Pela Atenção !!!

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63 The Model

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67 Average grain size ~ 5  m

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69 Govea-Alcaide et al. 2005

70 grains clusters weak links between clusters