Birefringence Enhancement Mechanism and Lattice Engineering Controlling Strategy of YPO4

doi:10.16553/j.cnki.issn1000-985x.2025.0078

Abstract

Abstract: Rare-earth phosphates are recognized as novel ultraviolet/deep-ultraviolet optical materials due to their wide bandgaps and excellent optical properties. In this work， two analogous structures （Ⅰ： ICSD No.24514 and Ⅱ： ICSD No.133671） of yttrium phosphate （YPO₄） crystals were identified through high-throughput screening of the inorganic crystal structure database （ICSD）. First-principles calculations were systematically employed to investigate the electronic structures and optical properties of these compounds. Computational simulations were conducted to verify the feasibility and reliability of regulating bandgap and birefringence in YPO₄ crystals through direct lattice parameter manipulation. The results demonstrate remarkable birefringence modulation under lattice engineering： full-dimensional lattice compression to 70% of the original size induced birefringence changes of 0.052 （phase Ⅰ） and 0.057 （phase Ⅱ） at 1 064 nm wavelength， while uniaxial compression along the c-axis （70% strain） yielded 0.029 （phase Ⅰ） and 0.031 （phase Ⅱ）. Both PO₄ and YO₈ groups were found to contribute significantly to the birefringence of YPO₄. Atomic-level analysis reveals that P and O atoms predominantly determine the birefringence orientation， whereas Y atoms play a crucial role in modulating the birefringence efficiency through lattice distortion. This systematic investigation confirms the effectiveness of lattice engineering in birefringence regulation， providing novel insights for designing advanced optical materials and expanding application scenarios for nonlinear optical crystals.

Key words: YPO₄ crystal; density functional theory; birefringence; lattice engineering; real-space atom cutting; Born effective charge

CLC Number:

TB34

HAN Yibo, JI Xu, JING Qun, ZHU Xuankai, AIZIZAIMU·WUBULITAYIER , ZHAO Wenhao, CAO Xinjia. Birefringence Enhancement Mechanism and Lattice Engineering Controlling Strategy of YPO₄[J]. Journal of Synthetic Crystals, 2025, 54(9): 1547-1557.

Figures/Tables 14

References 57

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Compound	ICSD number	Space group number	Space group symbol	Lattice constant/Å			Crystal system
Compound	ICSD number	Space group number	Space group symbol	a	b	c	Crystal system
Ⅰ	24514	141	I4₁/amd	6.876	6.876	6.186	Tetragonal
Ⅱ	133671	141	I4₁/amd	6.907	6.907	6.035	Tetragonal

Compound	ICSD number	Space group number	Space group symbol	Lattice constant/Å			Crystal system
Compound	ICSD number	Space group number	Space group symbol	a	b	c	Crystal system
Ⅰ	24514	141	I4₁/amd	6.876	6.876	6.186	Tetragonal
Ⅱ	133671	141	I4₁/amd	6.907	6.907	6.035	Tetragonal

Structure	Band gap/eV	Refractive index		Birefringence index
Structure	Band gap/eV	n_o	n_e	Δn（@1 064 nm）
Ⅰ	5.995 3	1.824 80	1.916 30	0.091 50
Ⅱ	6.019 7	1.828 96	1.918 91	0.089 94

Structure	Band gap/eV	Refractive index		Birefringence index
Structure	Band gap/eV	n_o	n_e	Δn（@1 064 nm）
Ⅰ	5.995 3	1.824 80	1.916 30	0.091 50
Ⅱ	6.019 7	1.828 96	1.918 91	0.089 94

Contribution	Structure	Scaling/%	Bond length/Å	n_e	n_o	Δn
PO₄	Ⅰ	100	1.548 10	1.629	1.535	0.094
		90	1.527 93	1.622	1.545	0.077
		80	1.498 47	1.608	1.531	0.077
		70	1.449 14	1.573	1.506	0.067
	Ⅱ	100	1.547 50	1.634	1.540	0.094
		90	1.526 80	1.617	1.542	0.075
		80	1.497 57	1.635	1.551	0.083
		70	1.446 71	1.592	1.527	0.065
YO₈	Ⅰ	100	2.288 05	1.745	1.626	0.120
		90	2.200 48	1.727	1.636	0.090
		80	2.080 60	1.716	1.626	0.090
		70	1.954 11	1.679	1.602	0.076
	Ⅱ	100	2.377 08	1.745	1.625	0.120
		90	2.202 65	1.726	1.634	0.092
		80	2.082 53	1.717	1.624	0.092
		70	1.953 62	1.676	1.604	0.072

Birefringence Enhancement Mechanism and Lattice Engineering Controlling Strategy of YPO₄

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Figures/Tables 14

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Atom	YPO₄-Ⅰ				YPO₄-Ⅱ
Atom	q_xx	q_yy	q_zz	Δq	q_xx	q_yy	q_zz	Δq
Y	3.857	3.857	4.165	0.308	3.853	3.853	4.165	0.312
P	3.354	3.354	4.386	1.032	3.354	3.354	4.379	1.025
O	-1.033	-2.573	-2.138	-1.105	-1.033	-2.571	-2.136	-1.103

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Contribution	Structure	Scaling/%	Bond length/Å	n_e	n_o	Δn
PO₄	Ⅰ	100	1.548 10	1.629	1.535	0.094
		90	1.542 04	1.616	1.530	0.086
		80	1.532 41	1.598	1.525	0.074
		70	1.520 44	1.590	1.533	0.057
	Ⅱ	100	1.547 50	1.634	1.540	0.094
		90	1.540 74	1.647	1.552	0.096
		80	1.530 93	1.632	1.550	0.082
		70	1.518 33	1.587	1.536	0.051
YO₈	Ⅰ	100	2.288 05	1.745	1.626	0.120
		90	2.281 63	1.740	1.622	0.118
		80	2.274 19	1.735	1.619	0.115
		70	2.212 46	1.729	1.621	0.108
	Ⅱ	100	2.377 08	1.745	1.625	0.119
		90	2.282 96	1.740	1.621	0.119
		80	2.273 11	1.733	1.619	0.114
		70	2.200 93	1.728	1.624	0.104

Contribution	Structure	Scaling/%	Bond length/Å	n_e	n_o	Δn
PO₄	Ⅰ	100	1.548 10	1.629	1.535	0.094
		90	1.542 04	1.616	1.530	0.086
		80	1.532 41	1.598	1.525	0.074
		70	1.520 44	1.590	1.533	0.057
	Ⅱ	100	1.547 50	1.634	1.540	0.094
		90	1.540 74	1.647	1.552	0.096
		80	1.530 93	1.632	1.550	0.082
		70	1.518 33	1.587	1.536	0.051
YO₈	Ⅰ	100	2.288 05	1.745	1.626	0.120
		90	2.281 63	1.740	1.622	0.118
		80	2.274 19	1.735	1.619	0.115
		70	2.212 46	1.729	1.621	0.108
	Ⅱ	100	2.377 08	1.745	1.625	0.119
		90	2.282 96	1.740	1.621	0.119
		80	2.273 11	1.733	1.619	0.114
		70	2.200 93	1.728	1.624	0.104