Li2co3

Li₂RuO₃ and Li₂Ru_0.5Sn_0.5O₃ were synthesised from RuO₂ (99.9% Alfa Aesar), SnC₂O₄ (98% Alfa Aesar) and Li₂CO₃ (99+% Merck) mixed in the appropriate ratios with 10% excess Li₂CO₃. Calcination was performed in air at 800 °C for 6 h, 900 °C for 12 h and then 1100 °C for 12 h with intermediate grinding. Li₂IrO₃ and Li₂Ir_0.5Sn_0.5O₃ were synthesised from IrO₂ (99.9% Alfa Aesar), SnO₂ (99.9% Alfa Aesar) and Li₂CO₃ (99+% Merck) mixed in the appropriate ratios with 10% excess Li₂CO₃. Calcination was performed in air at 1000 °C for 12 h and 900 °C for 36 h with intermediate grinding. The as-prepared materials were transferred to an Ar-filled glovebox and handled under inert atmosphere for all further manipulations. Li₂O₂ (95%, ACROS Organics) and KO₂ (Sigma Aldrich) standards were used as supplied.

Stoichiometric amounts of RuO₂ (Sigma-Aldrich, 99.9%) and SnO₂ (Sigma-Aldrich, 98%) were homogenized with a 10% wt excess of Li₂CO₃ (Sigma-Aldrich, purity 99.0%) to compensate its volatilization at high temperature. The resultant mixture was heated at 800 °C for 24 h with intermediate grinding. Furnace heating and cooling rates were maintained at 2 °C min⁻¹.

Nano-sized LTO was prepared through a solid-state reaction at 800 °C for 3 h after high-energy bead-milling between Li₂CO₃ (99.0%, Sigma-Aldrich, USA) and anatase TiO₂ (99.5%, Sigma-Aldrich, USA). Nano-sized LTO was placed in an autogenic reactor (316 stainless steel, Swagelok) with urea (99.0%, Sigma-Aldrich, USA) in the weight ratio of 5:1, and the cap was closed to isolate the reactor from the outer atmosphere. Coated LTO was obtained by heating the reactor to 700 °C at a heating and cooling rate of 10 °C min⁻¹ in an electric box furnace in air. (Note that an autogenic reactor used in this study was closed system).

The nanoparticles were prepared by sol-gel based Pechini method. Typically, LiCH₃COO·2H₂O (0.0075 mol), Mn(CH₃COO)₂·4H₂O (0.005 mol), and citric acid (0.02 mol) were dissolved in a mixed solvent (15 mL, 2:1 v/v distilled H₂O and ethylene glycol) while stirring to form a clear solution. Then, titanium (IV) isopropoxide (0.005 mol) was added dropwise to the above solution with stirring. The mixture was stirred vigorously at room temperature for 4 h and then heated to 140 °C to induce gelation. The obtained xerogel was further dried under vacuum at 120 °C for 10 h and then fired in air at 600 °C (heating rate: 2 °C min⁻¹) for 12 h. The Li_1.5MnTiO_4+δ nanoparticles was denoted LMTO-NP.
The bulk particles were prepared by a solid-state reaction method. Stoichiometric amounts of Li₂CO₃ (99.9%, Sigma-Aldrich), MnCO₃ (99.9%, Kojundo Chemicals), and TiO₂ (99.5%, Sigma-Aldrich) were mixed using a mortar. The resultant mixture was heated in an alumina crucible at 800 °C for 20 h at a heating rate of 2 °C min⁻¹. The Li_1.5MnTiO_4+δ bulk particles was denoted LMTO-BP.

The reactants used in this study were K₂CO₃ (≥99.0%, ~150 μm, Sigma-Aldrich), Na₂CO₃ (≥99.5%, ~10 μm, Sigma-Aldrich), Li₂CO₃ (99.997%, ~20 μm, Sigma-Aldrich), Nb₂O₅ (99.9%, ~2 μm, Sigma-Aldrich), Bi₂O₃ (99.9%, ~10 μm, Sigma-Aldrich), ZrO₂ (99.0%, ~5 μm, Sigma-Aldrich), and TiO₂ (≥99.9%, ~1 μm, Sigma-Aldrich), which are typically used in a conventional synthetic process. The carbonate powders of K₂CO₃, Na₂CO₃ and Li₂CO₃ were dried at 120 °C for 24 h before use owing to their hygroscopic characteristics. Also, all treatments of these powders, including weighing and drying, were carefully performed within a glove box filled with an Ar gas atmosphere. Stoichiometric Bi₂O₃-Na₂CO₃-TiO₂ and K₂CO₃-Na₂CO₃-Nb₂O₅ powder mixtures were used for the syntheses of pure BNT and KNN, respectively. The general chemical reactions of the reactants for the formation of BNT and KNN are as follows:


Additionally, their respective modified compositions were used as templates to assess the feasibility of preparing more complex compositions, specifically, 0.76BNT-0.04BLT-0.2BKT and 0.955KNN-0.03BNKLZ-0.015BNT, which were recently discovered to possess excellent piezoelectric properties35 36 . These modified oxides were prepared using the stoichiometric Bi₂O₃-Na₂CO₃-TiO₂-Li₂CO₃-K₂CO₃ and K₂CO₃-Na₂CO₃-Nb₂O₅-Bi₂O₃-Li₂CO₃-ZrO₂-TiO₂ powder mixtures, respectively.