Thermal analysis of phase transitions in PbZr1−xSnxO3 antiferroelectric single crystals
J Therm Anal Calorim
Thermal analysis of phase transitions in PbZr12xSnxO3 antiferroelectric single crystals
Irena Jankowska-Sumara 0 1 2 3
Jan Z_ ukrowski 0 1 2 3
Maria Podgo´rna 0 1 2 3
Andrzej Majchrowski 0 1 2 3
0 Institute of Applied Physics, Military University of Technology , ul. Kaliskiego 2, Warsaw , Poland
1 Institute of Physics, Pedagogical University of Cracow , ul. Podchora ̨ z_ych 2, Krako ́w , Poland
2 & Irena Jankowska-Sumara
3 Academic Center for Materials and Nanotechnology, AGH University of Science and Technology , Av. A. Mickiewicza 30, 30-059 Krako ́w , Poland
The combined thermal analysis techniques thermal expansion: and differential scanning calorimetry were used to characterize various phase transitions that exist in the solid solutions of PbZr1-xSnxO3. Using thermodynamic quantities, i.e., thermal expansion and specific heat to distinguish first-order transitions from second-order ones, we demonstrate that some perovskite antiferroelectrics can exhibit continuous transition at their Curie temperature TC. We observed such a transition in antiferroelectric crystals of solid solutions based on PbZrO3. Although pure PbZrO3 is a classical example of antiferroelectric crystal with a first-order transition at TC, the solid solutions of PbZr1-xSnxO3 in the range of composition of x [ 0.25 seem to exhibit a second-order phase transition.
Antiferroelectrics; Phase transitions; Specific heat; Thermal expansion
Introduction
PbZr1-xSnxO3 (PZS) belongs to the family of AB0B00O3
perovskite solid solutions based on well-known
antiferroelectric material PbZrO3. Phase diagram showing different
phases that exist in PZS with 0 \ x \ 0.4 obtained on the
basis of dielectric, optic and thermodynamic measurements
was already reported [
1
]. The substitution of Sn4? ions at
the Zr4? sites in PZS single crystals does not alter the basic
structure of PbZrO3 which crystallizes in an orthorhombic
structure at room temperature RT. The stability and range
of the existence of subsequent phases, namely A1
(orthorhombic)–A2 (orthorhombic)–IM (multiple cell
cubic)–PE (cubic), depend strictly on the composition.
Such rich phase diagram of PZS compound and its
potential possibilities of applications (especially the PZS
compounds enriched with Ti ions) have attracted the
interest of many researchers [
2–5
]. It was found that
mechanism of the A1–A2 phase transition is of purely
displacive character for all investigated compositions [6].
In a case of phase transition at TC, above x = 0.2 a gradual
change from order–disorder to displacive character also
takes place. Despite the efforts made, the nature of phase
transitions is still not clear. Numerous experiments
revealed distinct differences in physical properties of single
crystals with compositions of x below and above 0.25. It is
believed that all of this is due to the so-called tricritical
point, the existence of which was postulated in early
studies [
7
]. It means that around this concentration, the
change from the first- to second-order phase transition at
TC takes place. Simultaneously, the large value of the
dielectric permittivity at TC which is observed in both
PbZrO3 and PbZr1-xSnxO3 single crystals with x \ 0.25
considerably decreases in the compositions with x [ 0.25
and another intermediate phase—IM, called also ‘‘multiple
cell cubic’’ [
5
]— appears. In our earlier studies of specific
heat [
7
], we found that above the value of x = 0.25, the
latent heat at TC at PE–IM phase transition is absent
suggesting the change of the character of the phase transition
to a second order in these crystals. However, in this paper,
IM phase was erroneously identified as ferroelectric one. In
later studies, we found that this intermediate phase is
ferroelastic one [
1
]. Later, Brillouin scattering measurements
made in PbZr0.72Sn0.28O3 pointed to enhanced fluctuations
in coupling between local polarization and strain which
occurs due to Sn replacing in Zr-site [
8
]. Such large
fluctuations of order parameter are expected near the
secondorder phase transition, and electrostrictive coupling
between the strain and fluctuations of local polar regions
seems to be the origin of the anomalous behavior of the
temperature dependence of the relaxation time of this polar
regions—sLA [
8
].
Since all previous studies do not definitely prove that
second-order phase transition can exist in perovskite
materials with antiferroelectric phase transition, we
undertook a detailed study to be able to unequivocally
confirm the suggestion. For the purposes of this study
newly acquired high quality, transparent crystals were
selected for the experiment. Three crystals with values of
x chosen from different points of the phase diagram were
selected, namely 0.04, 0.09 and 0.3. The stoichiometry of
the compounds and thus quality of the crystals were
verified with X-ray photoelectron spectroscopy (XPS) and
energy-dispersive X-ray spectroscopy (EDS). Additionally,
the Mo¨ssb (...truncated)