PMN WITH PEROVSKITE AND PYROCHLORE STRUCTURE: COMPARISON OF DIELECTRIC PROPERTIES

1
PMN WITH PEROVSKITE AND PYROCHLORE STRUCTURE
COMPARISON OF DIELECTRIC PROPERTIES
S. Kamba, D Noujni, S. Denisov, V. Bovtun, S.
Veljko, M. Savinov, J. Hlinka and J.Petzelt
Institute of Physics, Academy of Sciences of
the Czech Republic, Na Slovance 2, 18221
Prague 8, Czech Republic kamba_at_fzu.cz M.
Dambekalne and A. Sternberg Institute of Solid
State Physics, University of Latvia, Kengaraga
str. 8, Riga, Latvia

• Experimental techniques
• Impedance analyzer HP 4192A
• (100 Hz 1 MHz, 5 - 900 K)
• Impedance analyzer HP 4291B
• (1 MHz 1.8 GHz, 100 550 K)
• Network Analyzer Agilent E8364B
• (50 MHz 50 GHz, 100 380 K)
• Time-domain THz spectrometer
• (100GHz 2.5THz, 10 950 K)
• Fourier Transform Infrared Spectrometer
• Bruker IFS 113 v (0.5 150 THz, 10 950 K)

Samples investigated PbMg1/3Nb2/3O3
perovskite Pm3m, a4.05 Å, Z1 Slater, Last
and Axe zone-center modes in perovskites
Pb1.83Mg0.29Nb1.71O6.39 pyrochlore Fd3m,
a10.6029 Å, Z8
Temperature dependences of spontaneous
polarization and indices of refraction in
perovskite PMN (after 1).
IR reflectivity of PMN perovskite (after 2).
IR reflectivity of PMN and PZN perovskite single
crystals (after 1).
Pyrochlore structure
Complex permittivity of PMN pyrochlore obtained
from the fit of IR reflectivity.
IR reflectivity of PMN pyrochlore ceramics.
Temperature dependence of complex permittivity of
PMN perovskite 3 and PMN pyrochlore taken at
various frequencies.
THz dielectric dispersion in PMN pyrochlore.
Temperature dependence of polar mode frequencies
in PMN perovskite 5.

• Conclusions
• PMN perovskite Typical relaxor ferroelectrics
• Broad and frequency dependent maxima of ?(T) and
  ?(T).
• Microwave relaxation slows down and broadens on
  cooling. The relaxation is the consequence of
  dynamics (flipping and breathing) of polar
  clusters.
• Ferroelectric soft mode in polar clusters splits
  below Burns temperature. A1 component hardens on
  cooling according to Cochran law.
• Anisotropic dielectric function of polar clusters
  was calculated.
• PMN pyrochlore Incipient ferroelectrics
• Permittivity increases monotonously on cooling.
• No dielectric dispersion observed between 100 Hz
  and 8.8 GHz.
• Temperature dependence of permittivity was
  explained by phonon softening.
• Burns and Dacol 1 published infrared spectrum
  of PMN pyrochlore instead of perovskite PMN.
• PMN pyrochlore phase can be distinguished
  spectroscopically from the perovskite phase.

PMN perovskite relaxor Frequency dependence o
complex permittivity at various temperatures
(after 3).
Effective medium approximation - Bruggeman
symmetrical formula for binary composites
References 1. G. Burns and F. H. Dacol, Sol.
State Commun. 48, 853 (1983). 2. S. A. Prosandeev
et al. Phys. Rev. B 70, 134110 (2004). 3. V.
Bovtun, S. Kamba et al. Ferroelectrics 298, 23
(2004). 4. J. Hlinka et al. Phys. Rev. Lett. 96,
027601 (2006). 5. S. Kamba et al. J. Phys.
Condens. Matter 17, 3965 (2005). 6. J. Hlinka et
al. Phase Transitions 79, 41 (2006).
Effective complex permittivity and components of
anisotropic dielectric function in PMN
perovskite polar clusters (after 4).