# Solvent-mediated hydrothermal synthesis of K/Bi-doped [Ba(1−x)Kx][Bi(1−y)Tiy]O3 perovskites: structure–property relationships and bandgap engineering

## TL;DR

Researchers synthesized a new type of perovskite material using a low-temperature method, finding that the solvent used affects its structure and properties, making it suitable for UV optoelectronic applications.

## Contribution

The study introduces an eco-friendly hydrothermal synthesis route for K/Bi-doped BaTiO3 perovskites with solvent-controlled structural and optical properties.

## Key findings

- Hexagonal perovskite structure formed with minor impurities like K2CO3 and Bi2Ti2O7.
- Solvent choice (water vs. ethylene glycol) significantly affects morphology and thermal stability.
- Direct bandgaps between 4.25 and 4.52 eV suggest potential for UV optoelectronic applications.

## Abstract

K/Bi co-doped BaTiO3 perovskites with composition [Ba(1−x)Kx][Bi(1−y)Tiy]O3 were synthesized using a hydrothermal method at 220 °C, employing either ethylene glycol (EG) or water as solvent. X-ray diffraction analysis with Rietveld refinement revealed a hexagonal perovskite structure (P63/m, a = b = 9.925 ± 0.008 Å, c = 7.285 ± 0.006 Å). Minor impurity phases (<5%) were identified as K2CO3 and Bi2Ti2O7. FTIR spectra confirmed the formation of metal–oxygen bonds such as Ba–O, Ti–O, and Bi–O. SEM images showed regular hexagonal morphologies for EG-derived samples and flake-like structures for water-derived ones. EDS analyses, complemented by ICP-OES elemental analysis, confirmed the elemental homogeneity. Thermo-gravimetric analysis indicated that EG-derived samples exhibited greater mass loss compared to water-based ones, attributed to endothermal processes and residual organic content (confirmed by CHN analysis). UV-vis spectroscopy showed absorption in the UV region with direct bandgaps ranging from 4.25 ± 0.06 eV to 4.52 ± 0.08 eV, calculated using Tauc plots. The structural characteristics, including perovskite symmetry with stereo chemically active Bi3+ ions and potential morphotropic phase boundary features, suggest these materials may be promising candidates for UV optoelectronic applications and potentially for ferroelectric devices, pending direct polarization measurements. This study presents an eco-friendly synthesis route for perovskite materials with tunable properties and offers insights into solvent effects on microstructure and stability.

Low-temperature hydrothermal synthesis of K/Bi-doped BaTiO3 perovskites with solvent-tunable properties. Water-synthesis yields high crystallinity and thermal stability; wide bandgaps (>4.0 eV) enable UV optoelectronic applications.