High pressure synthesis of lone-pair Universidad Complutense de Madrid, Departamento Física Aplicada III Rainer Schmidt High pressure synthesis of lone-pair electron Bi0.5Pb0.5CrO3 perovskite Ivan Pirrotta, Rainer Schmidt, Emilio Morán, Miguel A. Alario Universidad Complutense de Madrid Instituto de Ciencia de Materiales de Madrid (ICMM-CSIC) Department of Materials for Information Technologies Group of Electronic and Magnetic Materials and Heterostructures Solid State Chemistry Group Dpto. Química Inorgánica I Grupo de Física de Materiales Complejos Dpto. Fisica Aplicada III 20th June 2013 C-12

High pressure synthesis of lone-pair Universidad Complutense de Madrid, Departamento Física Aplicada III Rainer Schmidt High pressure synthesis of lone-pair electron Bi0.5Pb0.5CrO3 perovskite - Introduction: PbCrO3: Cr4+ BiCrO3 : Cr3+ - HP/HT synthesis - Bi0.5Pb0.5CrO3: Structural Characterisation of high and low-T phases Magnetic properties Dielectric properties - Conclusions

PbCrO3: structure & properties Introduction Rainer Schmidt PbCrO3: structure & properties 1967 2006 26-split (Pseudo)-cubic Random lone pair NON –FE Roth & De Vries J.Appl.Phys. 38 (1967) p.951. Cubic symmetry G-type AFM structure below TN = 245 K Arevalo-Lopez et al. J.Solid State Chem. 180 (2006) p.3271. Local and random orientation of the lone-pair electron, no long-range order No ferroelectricity Arevalo-Lopez et al. Inorg.Chem. 48 (2009) p.5434. Gradual spin reorientation between 185 K – 62 K 3

PbCrO3: structure & properties Introduction Rainer Schmidt PbCrO3: structure & properties Arevalo-Lopez et al. J.Solid State Chem. 180 (2007) p.3271. Compositional /displacive modulations of the Pb2+ cation HRTEM 4

BiCrO3: structure & properties Introduction Rainer Schmidt BiCrO3: structure & properties Sugarawa et al. J.Phys.Soc.Jpn. 25 (1968) p.1553. Synthesis of BiCrO3 @ 4 - 6 Gpa, Niitaka et al. Solid State Ionics 172 (2004) p.557. T > 440 K: Pnma orthorhombic T < 440 K: C2 monoclinic (centrosymmetric) (non-centrosymmetric, antiferroelectric) AFE order: G-Type below ≈115 K Guo et al. J. Mater. Res. 22 (2007) p.2081. La1-xBixCrO3 (x = 0.35) at ambient pressure FE below 77 K coexisting with AFM order Attfield et al. Chem. Mater. 21 (2009) p.2436. Bi1-xSrxCrO3 (x = 0.5) at ambient pressure x = 0.5 only single phase: Rhombohedral R(-)3c, Sr/Bi: Cr4+ & Cr3+ G-Type AFM with glassy component Semiconducting with variable range hopping 5

BiCrO3: structure & properties Introduction Rainer Schmidt BiCrO3: structure & properties Darie et al. Solid State Sciences 12 (2010) p.660. Gradual spin re-orientation between 80 K – 60 K 6

Synthesis Volume Conac ≈ x10 volume Belt Synthesis Rainer Schmidt Synthesis Bi1-xPbxCrO3 ( x = 0.25, 0.40, 0.5, 0.60, 0.75) Stoichiometric amounts of α-PbO, Bi2O3, Cr2O3 and CrO2 p = 40-70 kbar; T = 800-1000 ºC; t = 7-45 min Conac Press Volume Conac ≈ x10 volume Belt 7

Powder-XRD BiCrO3 Bi0.75-xPb0.25-yCrO3 Bi0.6-xPb0.4-yCrO3 Structural characterisation: high-T phase Rainer Schmidt Powder-XRD BiCrO3 Bi0.75-xPb0.25-yCrO3 Bi0.6-xPb0.4-yCrO3 Bi0.5Pb0.5CrO3 Bi0.4-xPb0.6-yCrO3 Bi0.25-xPb0.75-yCrO3 PbCrO3 22 31 40 49 58 67 76 85 94 103 2θ(°)

Room temperature phase Structural characterisation: high-T phase Rainer Schmidt Room temperature phase Bi0.5Pb0.5CrO3 Pbnm a = 5.4747(1) b = 5.4776(5) c = 7.7420(4) α = β = γ = 90°

HRTEM and CBED HRTEM image (B) CBED, mirror planes m1 and m2 FFT image Structural characterisation: high-T phase Rainer Schmidt HRTEM and CBED 5.5059 Å 5.5550 Å HRTEM image FFT image SAED Rectangle simulated image (B) CBED, mirror planes m1 and m2 (C) Full view of (B) (D) Calculated CBED for orthorhombic Pbnm: a2 x a2 x 2a

Powder X-ray thermodiffraction Structural characterisation: low-T phase Rainer Schmidt Powder X-ray thermodiffraction ≈ 150K structural transition occurs

Low temperature phase Bi0.5Pb0.5CrO3 P 2/m Pb,Bi O1 Cr O2 O3 Structural characterisation: low-T phase Rainer Schmidt Low temperature phase Bi0.5Pb0.5CrO3 P 2/m a = 3.805(1), b = 3.802(5) c = 3.806(9) a = b = 90° ; g = 90° 7’ Pb,Bi O1 Cr O2 O3

Magnetisation measurements Magnetic properties Rainer Schmidt Magnetisation measurements Magnetic susceptibility c vs T Magnetisation M vs applied field H

AC magnetic susceptibility measurements Magnetic properties Rainer Schmidt AC magnetic susceptibility measurements AC magnetic susceptibility c vs T AC magnetic susceptibility c vs T Frequency dependence of the spin relaxation time indicates a spin-glass behaviour

No magneto- capacitance Differentiated Mott-plot Dielectric properties Rainer Schmidt Impedance spectroscopy measurements Bi0.5Pb0.5CrO3 30 K ◊ Zero field ◊ 50 kOe ■ Circuit fit No magneto- capacitance ■ MR from circuit fits ■ e' , H = 0 from circuit fits (C1) ■ e' , 50 kOe from circuit fits (C1) ◊ Zero field ◊ 50 kOe -■- Circuit fit (a) (b) (c) (d) (e) Mott-hopping (f) Differentiated Mott-plot ■ H = 0 from circuit fits (R1) ■ 50 kOe from circuit fits (R1)

Conclusions Rainer Schmidt The solid solution: Bi1-xPbxCrO3 was prepared by means of high pressures and high temperatures synthesis For x = 0.5, we have obtained a new Cr4+/Cr3+ orthorhombic perovskite phase with disordered Pb/Bi in the A position Structure, Microstructure and symmetry were determined by XRD, ED and HRTEM, the structure transforms into a monoclinic phase at T < 150K Magnetic measurements indicate an AFM structure, spin canting, a spin glass component Magnetic field dependent dielectric measurements indicate perceptible magnetoresistance (up to 15%) but no magnetocapacitance. No ferroelectricity is indicated. Charge transport exhibits semiconducting temperature dependence and follows a Mott-type variable-range hopping (VRH) model.