Broadband Dielectric, Terahertz, and Infrared Spectroscopy of BaTiO₃–BaZrO₃ Solid Solution: From Proper Ferroelectric over Diffuse and Relaxor Ferroelectrics and Dipolar Glass to Normal Dielectric

Abstract

BaTiO 3 -xBaZrO 3 (BZT-x) solid solution represents the best-studied lead-free relaxor-ferroelectric (shortly relaxor) system with perspectives for piezoelectrics and electric field tunable microwave (MW) applications in a broad composition range. [1,2] Unlike usual lead-containing relaxors, they belong to isovalent solid solutions (Ti 4þ and Zr 4þ ions have the same valence) so that the quenched random electric fields, which play an important role in lead-containing relaxors, [3] are here not dominant. On increasing the Zr concentration x, it first undergoes the three first-order ferroelectric (FE) phase transitions (PTs) wellknown for barium titanate BaTiO 3 (BT), the best-known FE material. At T C % 400 K, BT undergoes predominantly displacive PT from the paraelectric cubic (C) perovskite structure to tetragonal (T) FE phase, near 270 K from T to orthorhombic (O) FE and near 180 K to rhombohedral (R) FE phase; for the general review and dielectric properties, see the studies by Lines and Petzelt [4,5] and references therein. For x % 0.11, the PTs merge into one diffuse FE transition and the behavior gradually changes into relaxor and finally dipolar glass one. BaZrO 3 (BZ) is a normal (slightly incipient FE) dielectric without any appreciable dielectric dispersion below the infrared (IR) phonon response. [6,7] Broadband dielectric spectroscopies up to terahertz (THz) and IR ranges are the most efficient experimental techniques for studying and understanding such rich properties. Namely, displacive proper FEs are characterized by an excitation whose frequency tends to zero on approaching the FE PT, socalled soft mode (SM), see the recent review [8] and references therein. Due to rather strong lattice anharmonicity (as is the case of BT), another overdamped excitation frequently appears below the SM frequency, so-called central mode (CM), which through mutual coupling takes over the SM softening close to T C . [8] Relaxor FEs (shortly relaxors) exhibit an additional relaxational (overdamped) excitation which appears below the SM-CM frequencies on cooling below so-called Burns temperature T B and characterizes the dynamics of the appearing polar nanoregions (PNRs), see the previous reviews [8,9] and references therein. This excitation softens typically from the MW range down to zero at so-called freezing temperature T f and creates the well-known frequency-dependent maximum T m > T f in the temperature dependence of the dielectric permittivity. Dipolar

Comparative study on phase transition behaviors of fractional molecular field theory and random-site Ising model

“…have the periodicity in spatial distribution on the crystal lattice or symmetry of space translation, such as barium titanate [1,2] and potassium dihydrogen phosphate [3,4] of ferroelectrics, as well as iron and nickel [5,6] of ferromagnets. While the second stage (approximately 1954 to now) mainly focuses on the macroscopic crystalline materials of component heterogeneous distribution, specifically the random distribution of some kinds of elements on the crystal lattice (no symmetry of space translation), also known as the crystals of component random distribution, such as lead magnesium niobate [7][8][9][10] and barium zirconate titanate [11,12] of ferroelectrics (including relaxorferroelectrics and dipole glasses), as well as gold iron, [13] bismuth manganese scandate [14,15] of ferromagnets (including relaxor-ferromagnets and spin glasses), etc. [16][17][18][19][20] After the first stage of researches, a gradually mature theoretical system for ferroelectric and ferromagnetic phase transitions in the crystals of uniformly distributed components has been established, including the phenomenological theories (Weiss molecular field theory, [21,22] Landau theory, [23] Devonshire theory, [24][25][26] etc.…”

Glassy Properties of the Lead-Free Isovalent Relaxor BaZr0.4Ti0.6O3

“…The lead-free BaZr x Ti 1−x O 3 (BZT) solid solution recently came into focus because of its possible conceptual proximity to magnetic spin glasses; since zirconium is isovalent to titanium, the random fields should be suppressed [11]. Structural investigations of BZT ceramics with various Zr concentrations, x, showed relaxor properties for 0.25 ≤ x ≤ 0.75 [12][13][14][15][16][17][18][19][20][21][22][23]. In a recent review paper, Petzelt et al [23] presented an infrared-range broadband dielectric study of a whole concentration range of the (1 − x)BaTiO 3−x BaZrO 3 Crystals 2023, 13, 1303 2 of 12 (BZT-x) solid solution.…”

“…Structural investigations of BZT ceramics with various Zr concentrations, x, showed relaxor properties for 0.25 ≤ x ≤ 0.75 [12][13][14][15][16][17][18][19][20][21][22][23]. In a recent review paper, Petzelt et al [23] presented an infrared-range broadband dielectric study of a whole concentration range of the (1 − x)BaTiO 3−x BaZrO 3 Crystals 2023, 13, 1303 2 of 12 (BZT-x) solid solution. They found different characteristic composition ranges, which included proper ferroelectric (x = 0), diffuse ferroelectric (0 < x ≤ 0.2), relaxor ferroelectric (0.4 ≤ x ≤ 0.8), dipolar glass (x > 0.8), and the standard dielectric (x = 1) properties.…”