Anisotropic dielectric response of lead zirconate crystals in the terahertz and infrared range at low temperature Tetyana Ostapchuk a *, Christelle Kadlec a , Petr Kuzel a , Jan Kroupa a , Vladimir Zelezny a , Jiri Hlinka a , Jan Petzelt a and Jan Dec b a Department of Dielectrics, Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic; b Institute of Materials Science, University of Silesia, Katowice, Poland (Received 16 May 2014; accepted 16 July 2014) Polarized terahertz transmittance and infrared reflectivity measurements were performed on selected lead zirconate crystals at T D 10 K. The fit of the spectra enabled us to obtain all three principal components of its anisotropic dielectric function and the corresponding parameters of the polar phonon modes. Keywords: antiferroelectrics; infrared and terahertz spectroscopy; lead zirconate; phonons; complex dielectric permittivity 1. Introduction Lead zirconate (PbZrO 3 ) (PZO) is a canonical antiferroelectric material, which still remains a challenging subject for studies.[14] Its orthorhombic Pbam (Z D 8) structure accommodates antiparallel shifts of the lead atoms in x- and x-directions as well as cor- related oxygen-octahedra rotations.[14] The orthorhombic x-axis coincides with the [110] pc or an equivalent direction (see, for example, [ 101] pc in Figure 1) of the high-tem- perature cubic lattice (the index pc stands for the pseudocubic reference lattice [4]). The bi-director macroscopic symmetry of the antiferroelectric order-parameter [5] may sug- gest a significant anisotropy of the macroscopic dielectric properties of the single-domain orthorhombic PZO and its dynamic response, but no relevant experimental evidence has been reported so far. In earlier dielectric studies,[6] performed on a PZO single-domain plate in a narrow temperature range around T C (»508 K), the authors measured the low- frequency dielectric permittivity only along one of the orthorhombic axes (z k [001] pc ). The permittivity values along the other two axes, corresponding to [1 10] pc and [110] pc directions, have not been reported so far. This is because the natural PZO crystals usually grow as platelets with large surfaces parallel to the pseudocubic planes (Figure 2) so that their response along two of the three orthorhombic axes cannot be measured by methods probing the out-of-plane response. In the present study we avoid this problem by performing electrode-less measure- ments of the in-plane response of PZO. For this purpose we use a standard Fourier trans- form infrared (FTIR) reflectivity and a time-domain terahertz (THz) transmission spectroscopy.[7] These optical methods make also possible to analyse the lattice modes involved in the antiferroelectric phase transition of PZO.[4] According to the factor-group analysis, 45 polar modes are expected to be IR-active in the antiferroelectric phase: 11 B 1u (z) C 17 B 2u (y) C 17 B 3u (x). Here x, y and z stand for the orthorhombic axes *Corresponding author. Email: ostapcuk@fzu.cz Ó 2014 Taylor & Francis Phase Transitions, 2014 Vol. 87, Nos. 1011, 11291137, http://dx.doi.org/10.1080/01411594.2014.953514