Lei Zhang,Zheng Cao,Qing-Qiao Fu,Chun-Yu Li,Ya-Qian Du,Yan-Nan Li,Ta La,Dai-Bing Zhang,Jun Wang
Yb 2 Ti 2 O 7 exhibits ferromagnetic and magnetic properties , which are expected to exert a discernible influence on the thermoelectric properties of SrTiO 3 composite. The La-Yb-Nb-doped SrTiO 3 powders, synthesized via the hydrothermal method , were prepressed and then buried in carbon powder before being sintered in a muffle furnace at 1573 K for 5 h. The Yb dopant precipitated during the sintering process, leading to the in-situ formation of Yb 2 Ti 2 O 7 . The content of Yb 2 Ti 2 O 7 increased with an increasing Yb concentration, resulting in a reduction in thermal conductivity and grain boundary potentials, and an increase in the peak electrical conductivity . The La and Nb dopants affect the electrical conductivity and the Seebeck coefficient. Therefore, by controlling the La, Nb, and Yb ratios, the La8Yb2Nb15 sample achieved the largest power factor ( PF ) value of 0.9 mWm −1 K −2 and a low thermal conductivity of 2.9 W m −1 K −1 , resulting in a high ZT value of 0.32 at 1000 K.
Rare-earth titanate pyrochlores have attracted considerable attention for their unique magnetic frustration. Among those compounds, Yb2Ti2O7, a candidate for quantum spin ice, has been extensively studied in its magnetic ground state. However, works on its dielectric property and structure-property relationship lag far more behind. Here, by preparing and investigating nonstoichiometric Yb2–xTi2O7−δ (x = 0–0.15) ceramics, we demonstrate that the samples with x ≤ 0.05 maintain a single-pyrochlore phase, but the nonstoichiometry arouses significant structural distortion and increased oxygen vacancy. As a result, the ferromagnetism, indicated by a positive Curie-Weiss temperature, decreases almost linearly with increasing x value. Remarkably composition-dependent low-temperature dielectric relaxations have been observed. In addition, through introducing nonstoichiometry, the relaxor degree of dielectric behavior is enhanced, and the dielectric curve shows an altered shape. The origin of this dielectric relaxation is attributed to the increased structural distortion reflected by the changed bond length/angle, since there is no phase transition in 90–300 K. Our work gives a comprehensive view on the structural, magnetic, and dielectric properties of Yb2Ti2O7, which is instructive for further work on pyrochlores.
Xingzhong Liu,Manting Zeng,Hua Hao,Zhonghua Yao,Hanxing Liu
This study proposes a novel grain-boundary engineering strategy that synergistically enhances both resistance against reduction and dielectric stability in BaTiO 3 -based ceramics sintered under reducing atmosphere. By constructing uniform 2–3 nm Yb 2 O 3 coatings on 100 nm BaTiO 3 particles via chemical co-precipitation, we achieve in situ formation of Yb 2 Ti 2 O 7 pyrochlore phases at grain boundaries during sintering. Unlike conventional solid-state processed counterparts, the grain-boundary-confined Yb 2 Ti 2 O 7 phases exhibit dual functional mechanisms: Zener pinning-induced ultrafine grain refinement, and lattice mismatch-generated compressive stress that stabilizes the pseudocubic phase. These coupled effects synergistically elevate carrier migration activation energies, enabling ultrahigh resistivity (7.91 ×10 10 Ω·cm) and exceptional resistance against reduction. Simultaneously, the synergy between stress and the grain structure refines ferroelectric domains to the nanoscale, thereby activating strong relaxor behavior that enhances dielectric stability. Consequently, the engineered ceramic simultaneously delivers X7R-compliant thermal stability ( ε 25℃ =1623, tanδ =0.76 %) and minimal DC bias dependence (∆ εᵣ/ε 0 = 4.2 % at 0–2 V/µm).
危险品化学品经营许可证（带存储）