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The Curie point of barium titanate (BaTiO3) has been a focal point of research since the discovery of its ferroelectric properties. Exploring methods to elevate the Curie point without relying on Pb as a dopant presents fresh opportunities for lead-free dielectric and/or piezoelectric materials. It is essential to avoid introducing ions like K + and Na + , which could jeopardize the functional ceramic characteristics. This study delves into the stoichiometry of barium titanate, examining how impurities, point defects and doping techniques influence its Curie point, focus on the potential of doping and processing to enhance this property. BaTiO3 nanopowders were synthesized directly with varying Ba:Ti ratios in an ethanol–water solution at 60∘C, followed by sintering at 1280∘C and characterization through dielectric spectroscopy. A comparison was made with samples doped with Si, vapor-doped with Bi and vapor-doped with Pb. Results revealed that even minimal Si doping could boost the ferroelectric properties and elevate the Curie point, while vapor-doping with trace amounts of PbO or Bi2O3 significantly increased the Curie point, particularly in samples with higher Ti content. The impact of vapor dopants of PbO and Bi2O3 was similar, with a nominal doping level of 1 mol% shifting the Curie point above 140∘C. Notably, in samples with a Ba:Ti ratio of 0.95 vapor-doped with PbO, the Curie point rose to 146∘C, a notable increase of 16∘C, surpassing the traditional doping efficiency. This study offers fresh insights into enhancing the Curie point of barium titanate-based materials, exploring the intricate connections among chemical stoichiometry, dopants, point defects and dielectric properties. It highlights the significant influence of chemical composition, impurities, defects and doping strategies on the dielectric characteristics of barium titanate. [ABSTRACT FROM AUTHOR]

The Curie point of barium titanate (BaTiO3) has been a focal point of research since the discovery of its ferroelectric properties. Exploring methods to elevate the Curie point without relying on Pb as a dopant presents fresh opportunities for lead-free dielectric and/or piezoelectric materials. It is essential to avoid introducing ions like K[Formula: see text] and Na[Formula: see text], which could jeopardize the functional ceramic characteristics. This study delves into the stoichiometry of barium titanate, examining how impurities, point defects and doping techniques influence its Curie point, focus on the potential of doping and processing to enhance this property. BaTiO3 nanopowders were synthesized directly with varying Ba:Ti ratios in an ethanol–water solution at 60∘C, followed by sintering at 1280∘C and characterization through dielectric spectroscopy. A comparison was made with samples doped with Si, vapor-doped with Bi and vapor-doped with Pb. Results revealed that even minimal Si doping could boost the ferroelectric properties and elevate the Curie point, while vapor-doping with trace amounts of PbO or Bi2O3 significantly increased the Curie point, particularly in samples with higher Ti content. The impact of vapor dopants of PbO and Bi2O3 was similar, with a nominal doping level of 1[Formula: see text]mol% shifting the Curie point above 140∘C. Notably, in samples with a Ba:Ti ratio of 0.95 vapor-doped with PbO, the Curie point rose to 146∘C, a notable increase of 16∘C, surpassing the traditional doping efficiency. This study offers fresh insights into enhancing the Curie point of barium titanate-based materials, exploring the intricate connections among chemical stoichiometry, dopants, point defects and dielectric properties. It highlights the significant influence of chemical composition, impurities, defects and doping strategies on the dielectric characteristics of barium titanate.

It has generally been believed that the reliability of BaTiO3‐based multilayered ceramic capacitors (MLCCs) is mainly contributed by hydroxyl (OH−), and the contribution of CO32− can be neglected. However, in this work, we demonstrated that the contributions of Ba/Ti ratio and CO32− play important roles in the delivering high reliability for BaTiO3‐based MLCCs. The structure and performance of MLCC devices and ceramic chips based on BaTiO3 powders prepared by different approaches were studied. It is found that the intracrystalline pores in ceramics or MLCCs are mainly derived from the decomposition of BaCO3 during sintering, which has been demonstrated by ceramic derived from hydrothermal method powder and its modified powders. The point defects of Ba and Ti vacancies mainly originating from nonstoichiometric Ba/Ti rather than thermally stimulated have substantial influence on the migration of grain boundary that determines the grain size and whether the pores can be annihilated from the bulk material. Particularly, the Ti vacancies have a strong pinning effect and inhibit the migration of grain boundary effectively, due to their shorter migration distance comparing to Ba vacancies. Therefore, the synergetic effect of the second phase BaCO3 and point defects leads to the differences in the structure and performance. [ABSTRACT FROM AUTHOR]

It has generally been believed that the reliability of BaTiO3‐based multilayered ceramic capacitors (MLCCs) is mainly contributed by hydroxyl (OH−), and the contribution of CO32− can be neglected. However, in this work, we demonstrated that the contributions of Ba/Ti ratio and CO32− play important roles in the delivering high reliability for BaTiO3‐based MLCCs. The structure and performance of MLCC devices and ceramic chips based on BaTiO3 powders prepared by different approaches were studied. It is found that the intracrystalline pores in ceramics or MLCCs are mainly derived from the decomposition of BaCO3 during sintering, which has been demonstrated by ceramic derived from hydrothermal method powder and its modified powders. The point defects of Ba and Ti vacancies mainly originating from nonstoichiometric Ba/Ti rather than thermally stimulated have substantial influence on the migration of grain boundary that determines the grain size and whether the pores can be annihilated from the bulk material. Particularly, the Ti vacancies have a strong pinning effect and inhibit the migration of grain boundary effectively, due to their shorter migration distance comparing to Ba vacancies. Therefore, the synergetic effect of the second phase BaCO3 and point defects leads to the differences in the structure and performance. [ABSTRACT FROM AUTHOR]

In this work, we investigate the influences of Ba/Ti ratio and sintering conditions on the characteristics of positive temperature coefficient of resistance (PTCR) and electrical properties of Ba m (Ti 1 − x Nb x )O3 (BTN) ceramics. The ceramics were fired at 1190 ∘ C for 0.5–6.0 h in a reducing atmosphere and then reoxidized at 600–650 ∘ C for 0–8 h. The Ba/Ti ratio (m) affected the electrical properties and PTCR effect of the BTN specimens. The room-temperature (RT) resistance of the BTN samples initially decreased (0. 9 9 4 < m < 1. 0 0 6) and then increased (1. 0 0 6 < m < 1. 0 1 8) as the Ba/Ti ratio increased. Moreover, BTN ceramics exhibit a pronounced PTCR effect, with a resistance jump greater by 3.0 orders of magnitude and a low 0.1  Ω RT resistance at a low reoxidation temperature of 600 ∘ C after sintering under a reducing atmosphere. Furthermore, the average sample grain size increased along with the Ba/Ti ratio. In addition, the influence of the sintering time and the reoxidation time on the electrical properties and the PTCR effect were also investigated. [ABSTRACT FROM AUTHOR]

Abstract: BaTiO3 nanoparticles with excess barium are directly synthesized from solution at 65°C. It is noted that a small amount of BaCO3 exists in the as-prepared samples. A series of standard mixtures with different proportion of BaTiO3 and BaCO3 are measured by XRD analysis to quantify the amount of BaCO3 in our synthesized samples. After a deduction of the amount of BaCO3, the concentration of excess barium in the lattice of BaTiO3 nanoparticles can be determined and the results show that the excess barium can reach a considerable concentration. The influences of defects and surfaces on BaTiO3 nanoparticles with excess barium are analyzed and two important reasons for the high concentration are also given. [Copyright &y& Elsevier]

Barium titanate nanoparticles with various nominal Ba/Ti ratios were prepared through direct synthesis from solution (DSS) and further annealed at different temperatures. Their deviation from stoichiometry was studied through XRD analysis, and a large deviation from stoichiometry has been observed. The grain size we studied ranges from 50 nm to 1 μm. For the as-prepared particles, the grain size is about 50 nm, and the maximum excess of Ti is over 15%. For the samples annealed at 800 °C, the grain size is increased to 100 nm, and the maximum excesses of Ba and Ti are 8 and 9%, respectively. The defects formed during synthesis and surface effect of nanoparticles are both estimated for their contributions to the deviation from stoichiometry, and the defects have been found to be mainly responsible for the large deviation observed. [ABSTRACT FROM AUTHOR]

Abstract: In an oxygen activity gradient, BaTiO3 ceramic generally relaxes twofold: a fast global relaxation in the oxygen sublattice and a sluggish in-grain relaxation in the cation sublattice(s), thus allowing one to simultaneously determine the two chemical diffusivities. [Yoo et al., J. Am. Ceram. Soc., 88, 617–623 (2005)]. Upon this ground, the chemical diffusivities have been measured, by a conductivity relaxation technique, on donor(LaBa •)-doped BaTiO3 ceramics with different Ba/Ti ratios, Ba1− x La x Ti1− x /4O3, Ba1−3x /2La x TiO3 and Ba1− x La x TiO3 all with x =0.01, against oxygen activity in the range of −15≤log(Po2/atm)≤0 at 1200 °C. It has been found that the chemical diffusivities for the cation sublattice(s), and those for oxygen as well, are essentially the same irrespective of the Ba/Ti ratios. This fact indicates either that only either of Ba or Ti is mobile or both have about the same mobility. Circumstantial evidences support the latter. [Copyright &y& Elsevier]

We report a simple and facile approach for the synthesis of semiconducting BaTiO 3 nanoparticles at low temperature using a direct solid state reaction between metal Ti and barium nitrate. The irregular large grain-sized Ba(NO 3) 2 and Ti powders can be converted into homogenous BaTiO 3 nanoparticles. The morphologies and structures of the BaTiO 3 nanoparticles can be facilely tuned. The semiconducting BaTiO 3 nanoparticles can be obtained at the condition of Ba/Ti ratio between 1:1 and1:3 just calcinated at 550 °C. The residual Ba(NO 3) 2 can be clear observed when Ba/Ti > 1:1, and titanium nitride appear when Ba/Ti~1:16.The reaction of synthesis of semiconducting BaTiO 3 nanoparticles starts at 550 °C. Under the suitable conditions, semiconducting BaTiO 3 nanoparticles can be prepared with the grain size~30 nm homogenously. During synthesis reaction, the transfer of N cation into Ti lattice is proposed for the mechanism of direct reaction between Ba(NO 3) 2 and Ti for synthesis of BaTiO 3 nanoparticles, which results in cation N decreases its valence and turns to an anion. Image 1084006 • Synthesized semiconducting BaTiO 3 nanopartiles at 550 °C. • Studied the effects of Ba/Ti ratio and reaction temperature. • Found cation-N transfers into Ti-lattice during synthesis. • Erected a synthesis mechanism for the direct reaction of Ti with Ba(NO 3) 2. [ABSTRACT FROM AUTHOR]