1. 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

2. 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

3. 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

4. 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

5. BiCrO3: structure & properties
Introduction Rainer Schmidt
BiCrO3: structure & properties
Sugarawa et al. J.Phys.Soc.Jpn. 25 (1968) p.1553.
Synthesis of 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

6. 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

7. 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 = kbar; T = ºC; t = 7-45 min
Conac Press
Volume Conac ≈ x10 volume Belt 7

8. 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
2θ(°)

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

10. HRTEM and CBED HRTEM image (B) CBED, mirror planes m1 and m2 FFT image
Structural characterisation: high-T phase Rainer Schmidt
HRTEM and CBED Å 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

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

12. 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

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

14. 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

15. 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)

16. 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.