BaTiO₃ nanoparticles of orthorhombic structure following a polymer precursor. Part I. X-ray diffraction and electron paramagnetic resonance

Abstract

BaTiO₃ nanoparticles were synthesized from a polymer template of Ba²⁺ and Ti⁴⁺ ions embedded in polymer molecules of polyvinyl alcohol. The polymer burns off upon heating in air at temperature as high as 450°C, resulting in a Pnma orthorhombic crystal structure for pure BaTiO₃ (o-BT-II). Distinct peaks appear in the X-ray diffractogram after 2 h of heating the sample at 550°C, with lattice parameters a = 0.6435 nm, b = 0.5306 nm, c = 0.8854 nm, and density ρ = 5.124 g cm⁻³. The usual tetragonal phase with a = 0.3994 nm, c = 0.4038 nm, and ρ = 6.012 g cm⁻³ appears as early as 650°C, with average crystallite size (D) growing as large as 25 nm from a value of 15 nm after 550°C. Two electron paramagnetic resonance signals occur for g ∼ 2.00 and 4.30 due to interstitial oxygen , or vacancies , and modified Ti⁴⁺ → Ti³⁺ (3d ¹) especially in the surfaces of small particles.

Acknowledgements

This work has been supported by a research grant from the Nanoscience and Technology Initiative of the Department of Science and Technology, Government of India.