Rapid Sintering of Li2O-Nb2O5-TiO2 Solid Solution by Air Pressure Control and Clarification of Its Mechanism

Abstract

We first successfully synthesized Li1+x−yNb1−x−3yTix+4yO3 (LNT) solid solutions (0.13 ≤ x ≤ 0.18, 0 ≤ y ≤ 0.06) rapidly at 1373 K for one hour under 0.35 MPa by the controlling of air pressure using an air-pressure control atmosphere furnace. The composition is a formation area of a superstructure for LNT, in which the periodical intergrowth layer was formed in the matrix, and where it can be controlled by Ti content. Therefore, the sintering time depended on Ti content, and annealing was repeated for over 24 h until a homogeneous structure was formed using a conventional electric furnace. We clarified the mechanism of the rapid sintering using various microscale to nanoscale characterization techniques: X-ray diffraction, a scanning electron microscope, a transmission electron microscope (TEM), a Cs-corrected scanning TEM equipped with electron energy-loss spectroscopy, and X-ray absorption fine structure spectroscopy.

Synthesis of Li–Ta–Ti–O new red phosphors with Mn⁴⁺ as activator and the relationship between photoluminescence intensity and crystal structure

“…The AAF can be controlled from 0.10 to 0.60 MPa; an oxygen concentration is corresponded to 0.211.13 atm. 5) We established a rapid sintering technique for Li 2 ONb 2 O 5 TiO 2 (LNT) solid solution using the AAF. 5) It was found that the optimal gas pressure was 0.35 MPa for LNT, and the superstructure with homogeneous periods was synthesized rapidly.…”

“…5) We established a rapid sintering technique for Li 2 ONb 2 O 5 TiO 2 (LNT) solid solution using the AAF. 5) It was found that the optimal gas pressure was 0.35 MPa for LNT, and the superstructure with homogeneous periods was synthesized rapidly. We considered that interstitial oxygen could promote oxygen diffusion with a combination of vacancies along the intergrowth layer, and accordingly, grain growth surprisingly improved by controlling air pressure.…”

“…This short time sintering has been reported about LNT. 5) In order to understand the mechanism of the high PL intensity, XANES was used to measure the LTT:Mn phosphors synthesized by EF and AAF. Figure 12 shows the XANES spectra of Mn K-egde for LTT:Mn phosphors synthesized by EF and AAF.…”

“…The AAF was developed jointly with a local company (FULL-TECH FURNACE CO., Ltd.), and succeeded in synthesizing the homogeneous materials in only 30 min. 5) Next, this unique material was applied to the host material of new phosphor doped rare-earths (RE 3+ : Eu, Er, Tb, Tm, or Dy). 6) Among them, the red phosphor of Eu 3+ doped LTT especially showed highly efficient red-light emission upon excitation at 399 nm, with an internal quantum efficiency of 98%.…”