Study on true congruent-melting LiNbO3 crystal growing with unity partition coefficients for any constituent species

2019 Fiscal Year Final Research Report

• Project/Area Number: 16H03855
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Crystal engineering
• Research Institution: Tohoku University
• Principal Investigator: UDA Satoshi 東北大学, 金属材料研究所, 教授 (90361170)
• Project Period (FY): 2016-04-01 – 2019-03-31
• Keywords: ニオブ酸リチウム / コングルエント / 化学量論 / 結晶化起電力 / イオン種 / 酸素 / 固液界面 / 熱力学自由度

Outline of Final Research Achievements

Combining a conventional concept of “congruent” with the essentially new concept of “stoichiometry”; a material whose activities of its constituent elements can be unity is stoichiometric, we have developed cs-MgO:LiNbO3 (Li2O:Nb2O5:MgO = 45.30:50.00:4.70) by introducing Mg and vacancy, both of which are simultaneously congruent and stoichiometric. Activities of all constituent elements can be unity so that the equilibrium partition coefficient, k0 of every chemical species in the melt is unity. Thus, they yield no segregation of ionic species during growth so that there is no compositional change in growing crystals even if they experience the unexpected perturbation, which is not possible in the conventional congruent LiNbO3 (c-LiNbO3). They are easy to growth with extremely homogeneous composition and are effective to achieve excellent nonlinear optical properties.

Free Research Field

結晶成長

Academic Significance and Societal Importance of the Research Achievements

酸化物融液からの結晶成長では最善の育成環境を整えても必ず非定常成長が起きる。結晶育成技術の限界である。この時、界面での局所平衡が損なわれイオン種偏析がある従来のコングルエント・ニオブ酸リチウム結晶（c-LN）では組成変動が起きる。しかし、「コングルエント＋化学量論」のニオブ酸リチウム結晶が成長する融液（cs-MgO:LN）ではイオン種偏析はないので組成変動はない。真のコングルエント成長である。本研究では成長速度の擾乱が生じても組成が均質で屈折率変動の非常に小さく次世代光学デバイスの作製やOEICの微細加工に十分耐えうる均質結晶を作製する新しいニオブ酸リチウム結晶を開発した。