硅酸盐学报

提拉法大尺寸晶体生长技术发展已逾百年，但由于生长界面处于高温、强电磁干扰、固液气三相共存的极端环境，很难原位获取界面热质输运状态。针对大尺寸铌酸锂晶体生长过程中实时监测界面失稳的难题，将4英寸光学级铌酸锂晶体的提拉速度、转速、功率等关键工艺参数，与界面相本征电动势(GEMF)的同步时间序列相建立一一映射，实现了工艺流程演化对生长界面热输运影响的全过程原位解析。GEMF分析结果发现了强烈的界面失稳现象，能够灵敏、实时、定量地反映界面温度波动规律、放肩过程的界面翻转失去质量，弥补了现有称量质量传感器和热电偶的盲区。建立GEMF与界面传热传质的关联模型，提出了一种原位评估大尺寸晶体生长界面稳定性的方法，为实现高品质大尺寸晶体的可控制备提供了理论依据和新颖技术路径。

Introduction Although the Czochralski method for large-size crystal growth has been developed for over a century, the in-situ acquisition of interface states becomes a challenge due to the extreme environment of high temperature, high pressure, strong electromagnetic interference, and the coexistence of solid, liquid, and gas phases. To address the challenge of real-time monitoring of interface instability during the growth of large lithium niobate crystals, we combined the temporal evolution of key process parameters such as pulling rate, rotation rate, and power-of a 4-inch optical-grade lithium niobate crystal with the synchronous time of its growth interface's intrinsic growth interface electromotive force(GEMF). This integration enabled a full-process in-situ analysis of how growth conditions affect the growth interface. The GEMF analysis revealed pronounced interface instability phenomena, which sensitively, quantitatively, and in real time reflect temperature fluctuations at the interface and the inversion phenomena during shoulder growth, thus filling the detection blind spots left by conventional load-cell sensors and thermocouples. In this work, a correlation model between GEMF and interfacial heat and mass transfer was established, and an in-situ method was proposed to evaluate the stability of the crystal growth interface, providing a crucial theoretical foundation and an innovative technical approach for the preparation of high-quality, large-size crystals. Methods For the synthesis of CLN polycrystalline powder, high purity(99.99%) materials of Li_2CO₃ and Nb_2O₅ in a molar ratio of 0.946 were mixed, ground and calcined. Afterwards, the ground mixture was molten in a platinum crucible in a CZ furnace. The key process parameters such as pulling rate, rotation rate and power of 4 in optical grade lithium niobate crystal were synchronously recorded together with the intrinsic growth interface electromotive force(GEMF), thereby establishing a quantitative correlation between GEMF signals and heat-mass transport. This approach enabled in-situ detection and real-time feedback control of interface instabilities, including temperature fluctuations and interface inversion, during the shoulder growth stage. The seed temperature(T_s) and crucible temperature(T_l) were monitored by thermocouples connected to a model Eurotherm 2404 thermometer(±0.1 ℃). Platinum wires were employed as leads and electrodes, with a positive electrode affixed to the seed and a negative electrode to the base of the platinum crucible. The GEMF between the growing crystal and the melt was measured by a model Keithley 2100 micro-voltmeter(±0.1 μV). Results and discussion The pronounced interface fluctuations and the intense interface inversion during the shouldering stage phenomena that are difficult to detect using conventional methods can be clearly determined. The validation with extensive production data from large-size crystals demonstrates that compared with conventional detection techniques, GEMF can provide real-time and valuable information on the interface state. Furthermore, a quantitative relationship between GEMF deviation and crystal mass loss is established and a feedback strategy for regulating interface stability is proposed via integrating GEMF measurements with time-series analysis of crystal growth parameters. Based on real-time trajectory analysis of heat and mass transfer during interface inversion, a control criterion for maintaining stable interface growth is established. During LN crystal growth, the GEMF trajectory can evolve smoothly along the reference trend represented by the Seebeck baseline, avoiding sharp deviations. When the G–T_s curve exhibits a tendency to deviate from the Seebeck baseline, it indicates that interface inversion is imminent. At this stage, reducing the rotation rate or enhancing the radial temperature gradient can suppress interface inversion and stabilize crystal growth. Conclusions In this study, the growth interface electromotive force(GEMF) technique was combined with the key process parameters such as pulling rate, crystal rotation rate and heating power to enable the in-situ diagnostics of the 4-inch lithium niobate(LN) crystal growth process. The results showed that the supercooling electromotive force component of the GEMF signal could accurately reflect the periodic temperature fluctuations at the crystal growth interface, which were identified as the primary cause of diameter deviations during the constant-diameter stage. Furthermore, GEMF measurements precisely captured the interface flipping phenomenon during the shouldering process. The quantitative relationships among electrical signal deviation, temperature fluctuation, and mass response were elucidated via establishing a simplified one-dimensional heat-mass transport model for the boundary layer. Local fluctuations in heat flux could induce thermal-equilibrium shifts at the interface, thereby affecting crystallization rate and mass stability. Compared with conventional monitoring methods, the proposed model enabled real-time mapping from electrical signals to the physical growth state, providing an effective technical approach for elucidating interface instability mechanisms, predicting crystallization quality deviations, and constructing closed-loop feedback control systems for the interface. This methodology could have a significant promise for the controllable growth of large-size, high-quality crystals.