	US 12,321,080 B2
	Domain wall straightening method of periodically poled ferroelectric crystal
Xiaoling He, Guilin (CN); Weidi Zhao, Guilin (CN); Xudong Song, Guilin (CN); Haitao Zhou, Guilin (CN); Changlong Zhang, Guilin (CN); Wenyuan Wu, Guilin (CN); Yanbin Zuo, Guilin (CN); and Jinliang Wang, Guilin (CN)
Assigned to Guilin Bairui Optoelectronics Technology Co., Ltd., Guilin (CN)
Filed by Guilin Bairui Optoelectronics Technology Co., Ltd., Guilin (CN)
Filed on Jan. 11, 2025, as Appl. No. 19/017,542.
Application 19/017,542 is a continuation of application No. PCT/CN2024/108721, filed on Jul. 31, 2024.
Claims priority of application No. 202410964422.4 (CN), filed on Jul. 18, 2024.
Prior Publication US 2025/0147384 A1, May 8, 2025
Int. Cl. G02F 1/355 (2006.01)

CPC G02F 1/3558 (2013.01) [G02F 1/3551 (2013.01)]

4 Claims

1. A domain wall straightening method of a periodically poled ferroelectric crystal, comprising the following steps:

step 1: making a negative polarity surface of a sample to be poled upward by a quasi-static test method, with a piezoelectric coefficient of d_s, and d_s>0, and then periodically poling the sample;

placing one surface of the poled sample on an insulating plate for testing a piezoelectric coefficient d_c, and then placing the sample on the insulating plate in reverse for testing a piezoelectric coefficient d_r;

when the absolute values of d_cand d_rare both greater than d_s/2, continuing to pole the sample;

when the absolute value of the tested piezoelectric coefficient is less than d_s/2, if a difference in the absolute values of d_cand d_ris less than 20%, judging that a poled reversed domain penetrates through the entire crystal, and obtaining a domain penetrated crystal for use;

if the difference in the absolute values of d_cand d_ris greater than 20%, judging that the reversed domain does not penetrate through the entire crystal, stopping the poling, conducting single domain for the sample, and conducting periodic poling again;

step 2: placing the domain penetrated crystal in step 1 upward in the original negative polarity direction instead of on the insulating plate by the quasi-static test method, and testing a piezoelectric coefficient d_p;

step 3: calculating the duty cycle of a test region by a formula D=(d_p+d_s)/2d_s; wherein if d_p>0, the duty cycle of the reversed domain is 1-D, which indicates that the area of the reversed domain region is smaller than the area of an unreversed domain region, and if d_p<0, the duty cycle of the reversed domain is D, which indicates that the area of the reversed domain region is larger than the area of the unreversed domain region;

step 4: selecting multiple points on the poled sample for testing the piezoelectric coefficient, and calculating the duty cycle distribution condition of different regions of the poled sample according to step 3;

step 5: according to the results obtained from step 3, if the duty cycle D is greater than a designed duty cycle by 20%, conducting single domain for the sample and conducting periodic poling again; and if the duty cycle D is greater than 0 but less than 20% than the designed duty cycle, continuing to pole the sample, and adjusting the size of poling voltage according to the change quantity Δd_pof the piezoelectric coefficient d_p;

step 6: testing equidistant regions on a same coordinate axis; if 2%d_s≥Δd_p≥0.5% d_sin any region, indicating that the transverse growth rate of reversal is in a reasonable range, and indicating that the domain wall tends to be flat; and according to step 5, judging whether to continue poling, and finally making the duty cycle D and the designed duty cycle reach an error range of ±0.5%;

if Δd_p>2% d_sin any region, reducing the voltage; taking out the sample after poling for testing the piezoelectric coefficient; and repeating the above calculation to judge whether to continue the poling until the duty cycle reaches 50%;

if Δd_p<0.5% d_sin any region, increasing the voltage; taking out the sample after poling for testing the piezoelectric coefficient; and repeating the above calculation to judge whether to continue the poling until the duty cycle reaches 50%.