Structural, electrical and spectroscopic studies of the diffuse phase transition relaxor-like ferroelectric material Ba[(Ho,Sb)_0.05Ti_0.9]O₃

Abstract

Spectroscopic, structural and electrical properties of Ba[(Ho,Sb)_0.05Ti_0.9]O₃ have been characterized to determine the effects of charge compensated dipole-like (Ho³⁺_, Sb⁵⁺) substitutions on temperature dependent material properties. XRD and Rietveld analysis have been used to determine lattice parameters and coefficients of thermal expansion from RT to 1373 K. Capacitance measurements have been conducted over the temperature range [198 K, 1073 K] and frequency range [10 Hz, 1 MHz] to investigate the dielectric properties, including Curie temperature. The microstructural features of the material, observed using a scanning electron microscope, show submicron grain size. The oxidation states of Ho³⁺ and Sb⁵⁺ substitutions within Ba[(Ho,Sb)_0.05Ti_0.9]O₃ have also been indirectly investigated using X-ray photoelectron spectroscopy and are reported in relation to the observed Ti 2p spectrum. Ba[(Ho,Sb)_0.05Ti_0.9]O₃ has a maximum relative permittivity of about 5000 at 267 K that corresponds to an orthorhombic ($\mathit{\text{Pmmm}}$) to tetragonal (P4/mmm) phase transition. Another structural phase transition of Ba(Ho_0.05Sb_0.05Ti_0.9)O₃, from tetragonal (P4/mmm) to cubic ($Pm\overline{3}m$), is observed between 623 K and 673 K through a peak in the dielectric constant as well as Rietveld refinement of XRD data. Thus, charge compensated dipole-like (Ho³⁺, Sb⁵⁺) substitutions within BaTiO₃ result in the formation of a solid solution as observed through the material Ba[(Ho³⁺,Sb⁵⁺)_0.05Ti_0.9]O₃. Compared with BaTiO₃, the material possesses some similar properties, like the same structural sequence $\mathit{\text{Pmmm}}\to P4/mmm\to Pm\overline{3}m$ with increasing temperature, yet other properties, like diffuseness of the temperature dependent relative permittivity, are fundamentally different and consistent with a dipole-like glass state. Experimental results are compared with several currently utilized models in an effort to better understand the effect that dipole-like substitutions have on material properties.

KEYWORDS:

• Lead-free ferroelectric barium-titanate
• diffuse phase transitions
• dipole engineering at the nanoscale
• temperature dependent x-ray diffraction and relative permittivity
• Curie temperature
• dipole-like glass state
• thermal expansion coefficients (TEC)
• x-ray photoelectron spectroscopy