Abstract
In the last two decades, variably doped strontium barium niobate (SBN) has attracted a lot of scientific interest mainly due to its specific non-linear optical response. Comparably, the parental compound, i.e., undoped SBN, appears to be less studied so far. Here, two different cuts of single-crystalline nominally pure strontium barium niobate in the composition Sr0.61Ba0.39Nb2O6 (SBN61) are comprehensively studied and analyzed with regard to their photoconductive responses. We present conductance measurements under systematically varied illumination conditions along either the polar z-axis or perpendicular to it (x-cut). Apart from a pronounced photoconductance (PC) already under daylight and a large effect upon super-bandgap illumination in general, we observe (i) distinct spectral features when sweeping the excitation wavelength over the sub-bandgap region as then discussed in the context of deep and shallow trap states, (ii) extremely slow long-term relaxation for both light-on and light-off transients in the range of hours and days, (iii) a critical dependence of the photoresponse on the pre-illumination history of the sample, and (iv) a current–voltage hysteresis depending on both the illumination and the electrical-measurement conditions in a complex manner.
Highlights
Published: 3 July 2021The solid solution strontium barium niobate (Sr1− x Bax Nb2 O6, SBN) constitutes a fascinating material system, exhibiting a plethora of functional properties
The compound, which crystallizes in the tetragonal tungsten bronze (TTB) structure for 0.25 < x < 0.8 [3], has attracted a great deal of interest of different scientific communities within physics, chemistry, and materials research
We focus on the pronounced photoconduction of undoped SBN
Summary
The solid solution strontium barium niobate (Sr1− x Bax Nb2 O6 , SBN) constitutes a fascinating material system, exhibiting a plethora of functional properties These are highly sensitive to a number of internal (exact chemical composition, i.e., the value of x; doping by rare earth and/or transition metal ions [1], variation of oxygen content [2]) and external (electric, photonic, strain fields) stimuli and being effectively tunable for potential applications. Huge effort has been dedicated to exploring, optimizing, and exploiting the nonlinear optical, electrooptic, and photorefractive properties, which form the basis for applications such as holographic data storage or electro-optic modulation In this context, mainly the congruently melting composition Sr0.61 Ba0.39 Nb2 O6 (SBN61) doped with some selected ions such as cerium or chromium for enhancing the photorefractive response, and–to some lesser extent–the composition Sr0.75 Ba0.25 Nb2 O6 (SBN75), exhibiting a maximum linear electro-optic coefficient r33 , have been in the focus.
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