Nb2o5

Nb₂O₅, K₂CO₃, n-Propylamine, dopamine (DA), N-methyl-2-pyrrolidone (NMP), poly-vinylidene fluoride (PVDF), and conductive carbon black were purchased from Sigma-Aldrich. A liquid electrolyte consisting of 1 M LiPF₆ in ethylene carbonate/dimethyl carbonate/ethyl methyl carbonate (1/1/1, weight ratio) with the addition of 1 wt% vinylene varbonate was provided by Shenzhen Kejingstar Technology Ltd. (Shenzhen, China). Deionized water was used in all experiments, and all of the chemicals were used without being further purified.

The precursors used were Nb₂O₅ (99.9% purity, Sigma-Aldrich, St. Louis, MO, USA), Ta₂O₅ (99.0% purity, Sigma-Aldrich), Sb₂O₅ (99.9% purity, Alfa Aesar, Haverhill, MA, USA), Na₂CO₃ (99.5% purity, Panreac M&E, Barcelona, Spain), K₂CO₃ (99.0% purity, Fisher Scientific, Hampton, NH, USA) and Li₂CO₃ (99.5% purity, Panreac M&E). These precursors were attrition-milled individually in a Fritsch Pulverisette 7 planetary ball using ZrO₂ stabilized with Y₂O₃ balls in ethanol during 2 h. This grinding step homogenized the particle size of the different powders between 2 and 10 μm. The powders obtained were oven dried at 80 °C for 24 h, were mixed according to the stoichiometry of the (K_0.44Na_0.52Li_0.04)(Nb_0.82Ta_0.10Sb_0.04)O₃ formula and were attrition-milled again for 2 h.

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.

High-purity and finely powdered tantalum pentoxide (Ta₂O₅, Sigma-Aldrich (St. Louis, MO, USA) 99.99% trace metals basis, <20 µm) and niobium pentoxide (Nb₂O₅, Sigma-Aldrich, 99.9% trace metals basis, −325 mesh) were used as the starting materials. Polyvinyl alcohol/[poly (vinyl butyral-co-vinyl alcohol-co-vinyl acetate)] (PVB/PVA), Sigma-Aldrich, average MW = 50,000–80,000 by gel permeation chromatography (GPC) and poly (ethylene glycol, PEG, Sigma-Aldrich, average MW = 200) were used as the binder to prepare the powder mixture. Finally, the powder mixture was homogenized in a ball miller for 4 h and the slurry was dried (under a heat lamp) over a period of ~36 h.

The defective Ti₂Nb₁₀O_29–x was fabricated through a one-step solid-state reaction using TiO₂ (Sigma–Aldrich, 99.9%) and Nb₂O₅ (Sigma–Aldrich, 99.9%) with a predetermined molar ratio of TiO₂ : Nb₂O₅ = 2 : 5. These precursors were mixed and milled by a ball-milling machine (SPEX 8000M) for 4 h, and finally calcined at 1200 °C for 4 h in a tube furnace in an argon atmosphere. As a comparison, the stoichiometric Ti₂Nb₁₀O₂₉ was also synthesized by the same process except for the calcination in an air atmosphere.
To prepare the Ti₂Nb₁₀O_29–x and Ti₂Nb₁₀O₂₉ samples for electronic conductivity measurements, the above precursors were uni-axially pressed into pellets with a diameter of 10.25 mm at a pressure of 1000 kg cm^–2. The pressed pellets were calcined at 850 °C for 5 h and then at 1200 °C for 48 h in argon (for Ti₂Nb₁₀O_29–x) or air (for Ti₂Nb₁₀O₂₉). After polishing the two sides of the calcined pellets, gold films were evaporated onto both sides, forming Au/Ti₂Nb₁₀O_29–x/Au and Au/Ti₂Nb₁₀O₂₉/Au symmetric ion blocking cells.

0.7BiFe₁–_xNb_xO₃–0.3BaTiO₃ (x = 0, 0.005, 0.01, 0.02, 0.03, 0.04 and 0.05) ceramics were synthesized by the solid-state reaction method using Bi₂O₃ (99%), Fe₂O₃ (99%), BaCO₃ (99%), TiO₂ (99%) and Nb₂O₅ (99.99%) powders (Sigma-Aldrich, Gillingham, UK). The precursor powders were weighed out according to the required stoichiometry, followed by mixing and milling in propan-2-ol with yttria-stabilized zirconia media for 24 h and drying for 12 h at 90 °C. Afterwards, the powders were calcined at 800 °C for 4 h in air and milled again for 24 h. An addition of 2 wt% polyethylene glycol (PEG) lubricant was made into the dry calcined powders. Green pellets, 10 mm in diameter, were prepared by uniaxial pressing at a pressure of 100 MPa. The ceramic pellets were then sintered in a covered alumina crucible at 1010 °C for 3 h with heating and cooling rates of 5 °C/min. Conductive electrodes were applied using a silver paste (C2130823D1, Gwent Electronic Materials Ltd., Pontypool, UK), which was heated to 550 °C for 30 min for densification.