摘要
利用二级轻气炮加载下的冲击Hugoniot线(冲击波速度D-粒子速度u关系)和粒子速度剖面测量,结合基于密度泛函理论的平面波赝势计算研究了z切LiTaO3单晶的高压相变.实验发现,D-u关系在u=0.95km/s附近出现明显拐折;实测波剖面中25.9GPa和32.6GPa时观测到弹-塑性双波结构,而终态压力为42.7GPa和53.0GPa时则为三波结构.上述结果都清楚地表明z切LiTaO3单晶冲击相变的发生,相变起始压力约为37.9GPa.同时,理论计算的菱形相(R3c对称群)压缩线与低压实验数据符合较好,而正交相(Pbnm对称群)压缩线则与扣除热压贡献的高压实验数据相符,由此推断z-切LiTaO3的高压相为正交结构.从实验和理论上澄清了z切LiTaO3的相变起始压力和高压相晶体结构的认识,研究工作亦对类似单晶材料的冲击相变研究有参考价值.
High-pressure phase-transition behaviors of z-cut lithium tantalate single-crystal have been studied by Hugoniot measurements at our two-stage light-gas gun and DFT-PWP calculations.A distinct discontinuity was discovered on the D-u（shock-wave velocity versus particle velocity）relation.An elastic-plastic two-wave structure was observed from the VISAR measured particle velocity profiles at low pressures（25.9 GPa and 32.6 GPa）,while three-wave structure appeared in the measured particle velocity profiles at the final pressure of 42.9 GPa and 53.0 GPa.Both facts indicate a shock-induced phase transition of LiTaO3 samples occurred with an onset pressure of 37.9GPa.The theoretically calculated 0K pressure versus compression ratio（P-V/V0）curve for the rhombohedral phase（R3c space group）is in good agreement with the low-pressure experimental data,while that for orthorhombic phase（Pbnm space group）is in accord with the results by deducing thermal pressure contribution from the measured shock-compression data at high pressures.This suggests that the high-pressure phase has orthorhombic symmetry.High-pressure phase transformation behaviors including the transition pressure and structures,which are unclear in current literature,have been clarified in this paper by our new shock-wave data and ab-initio calculations.These behaviors were demonstrated to be in close similarity with that of its isomorphous crystal LiNbO3.The present work is significant for the investigations of shock-induced phase-transition of similar single-crystal materials.
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
2007年第11期6557-6564,共8页
Acta Physica Sinica
基金
中国工程物理研究院科学技术基金(批准号:20050102)资助的课题.~~
关键词
z-切LiTaO3
冲击诱导相变
冲击波实验
第一性原理计算
z-cut LiTaO3 single-crystal,shock-induced phase-transition,shock-wave experiment,ab-initio calculation
