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

Apresentação em tema: "11 Renato F. Jardim Instituto de Física Universidade de São Paulo Brazil Novos Óxidos Metálicos com Propriedades Eletrônicas Interessantes Maringá, Setembro."— Transcrição da apresentação:

1 11 Renato F. Jardim Instituto de Física Universidade de São Paulo Brazil Novos Óxidos Metálicos com Propriedades Eletrônicas Interessantes Maringá, Setembro de 2011

2 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

3 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 4 Manganites - La 1-x Ca x MnO 3 La 0.7 3+ Ca 0.3 2+ Mn 0.7 3+ Mn 0.3 4+ 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

5 55 Tabela Periódica Alcalino Metal 3d Terra Rara O, Cl, F General Formula A 1-x A’ x BO 3

6 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

7 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 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 ???

9 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 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 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 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 13 Magnetorresistência Colossal La 0.6 Y 0.1 Ca 0.3 MnO 3 Electronic Properties Applying a Magnetic Field Sensor !!!

14 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 15 Electronic Properties Applying Pressure La 0.7 Ca 0.3 MnO 3 Sensor !!!

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

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

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

19 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 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 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 22 Caso Extremo – Separação Intra & Intergranular Sm 1.8 Ce 0.2 CuO 4-y Efeitos de Granularidade !!! (Restrições para Aplicações Tecnológicas !)

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

24 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 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 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 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 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 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 operating @ 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 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 31 ● J c (77 K, 0 T) ~ 70x10 3 A/cm 2 - filaments (1999) ● J c (77 K, 0 T) ~ 15x10 3 A/cm 2 - 10 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 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; ● Properties @ very high B (B < 14 T) are well studied ● How about the transport properties @ very low B (B < 70 mT) ? ● The data @ 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 Properties @ very low B (B < 70 mT) ● Transport Properties @ very high B (B < 18 T) ● Transport Barkhausen-like noise @ B < H c1 Experimental

33 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 (Air) @ 750 ºC (40 h); @ 800 ºC (40 h); @ 850 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 Treatment @ 850 ºC (40 h) – After Pressuring !!! Summary of the Pressuring Process

34 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 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 36 XRD Powder Diffraction Data taken mostly on pellets ! Powder Sample BP5 BP4 BP3 BP2 Lotgering factor F(00l)

37 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 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 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 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 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 42 Three-level superconductivity system Critical Current Data + Virgin curves + Returning curves B max + ????Flux-trapping curves Dois “Plateaus”

43 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 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 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 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 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 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 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 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 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 52 Some Barkhausen-noise data J/J c (0) 0.8 0.7 0.6 0.5 0.4 ● The noise occurs at ≠ “time” when the sample is subjected to ≠ J/J c (0)

53 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 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 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 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 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 58 Laboratório de Estado Sólido e Baixas Temperaturas Medidas de propriedades magnéticas (SQUID) Bobinas supercondutoras ~ 7 Tesla Temperatura 2K < T < 300K

59 59 Onde me encontrar………. OOPSSS !!! rjardim@if.usp.br

60 60 Muito Obrigado Pela Atenção !!! rjardim@if.usp.br

61 61

62 62

63 63 The Model

64 64

65 65

66

67 67 Average grain size ~ 5  m

68 68

69 69 Govea-Alcaide et al. 2005

70 70 grains clusters weak links between clusters