A defect pyrochlore-like acentric cubic lead titanium-tellurate crystal exhibiting strong second harmonic generation activity and an extended transparent window

Abstract

Non-centrosymmetric (NCS) oxides have attracted considerable attention owing to their versatile applications in the optoelectronic field. However, tailoring oxide-based NCS crystals with a wide transparency range remains a challenge. Here, we present an acentric cubic lead titanium-tellurate crystal Pb₄Ti₃TeO₁₃ (PTTO), identified via spontaneous crystallization using the traditional pyrochlore structure as a template. Notably, PTTO features a defect pyrochlore-like structure, characterized by the presence of distorted [Ti/TeO₆] octahedra and [PbO₇] polyhedra, endowing it with a strong second harmonic generation (SHG) activity of about 0.4 × AgGaS₂. More importantly, the notable merit of heavy elements Pb and Te lies in their inherently low phonon energy, which effectively redshifts the infrared (IR) transmission cutoff edge exceeding 7.6 μm, thereby surpassing the majority of previously reported tellurate-based acentric crystals. Additionally, a combination of theoretical and structural analyses was employed to elucidate the origin of optical activity in PTTO. These findings inspire a way to extend the IR transmittance range of oxide nonlinear optical crystals with enhanced SHG efficiency.