Reversed domain configuration behavior in BaMgF 4 ferroelectric crystal
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Piezoresponse mode atomic force microscopy was used to induce a dynamic polarization reversal process and to characterize domain configuration behavior in BaMgF4 single crystal. Triangular reversed domains observed on the polar and non-polar surface demonstrate a sideways domain wall motion mechanism prevailing in the switching process of the bulk BaMgF4 crystal. The domain wall bowing phenomenon due to the strong pinning of the crystal defects was first visualized in the piezoresponse image of the engineering domain pattern in BaMgF4 crystal.
I. INTRODUCTION
Fluoride BaMgF4 single crystal has become a promising candidate for ultraviolet frequency conversion because it is transparent for wavelengths less than 140 nm, is resistant to solarization, and can be used for quasiphase-matched interactions, which eliminates Poyntingvector walk-off.1 Such excellent features are predominant over those of the conventional optical ferroelectric crystal like LiNbO3 and LiTaO3 for the second-harmonic generation (SHG) in the ultraviolet and vacuum ultraviolet (UV/VUV) region; the latter is restricted to the lower wavelength transparency cutoff limited to 330 nm (LiNbO3) and 280 nm (LiTaO3). The SHG effect is closely related to ferroelectric domain stability in the electric field-driven spontaneous polarization reversal. In such a dynamic process of domain formation, the intrinsic factors determining the shape of the elementary nucleus and the final contour of grown domains may be derived from ferroelectric crystal symmetry, anisotropy of the wall energy density, and fine mechanisms of the domain wall motion. Thus, observation of the switched domain configurations is necessary and provides direct insight into understanding domain nucleation and growth behavior. Here we report a direct visualization of different reversed-domain configuration behaviors in BaMgF4 (BMF) single crystal induced by atomic force microscopy (AFM). Ferroelectric domain wall bowing phenomena are first presented in the BMF crystals. The lateral AFM tip field-induced sharp, wedgelike 180° reversed
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0124 1072 J. Mater. Res., Vol. 22, No. 4, Apr 2007 http://journals.cambridge.org Downloaded: 17 Apr 2015
domains on the non-polar surface of BMF crystal are also shown in the present study.
II. EXPERIMENTAL
Ferroelectric BaMgF4 single crystals were directly grown from the melt by the Czochralski technique.2 The crystals were processed into polished thin plates with various thicknesses. Domain switching was performed by applying bias using a conductive probing tip. A computer-controlled program was used to apply voltage pulses to the BMF sample for domain patterns via a platinum/titanium-coated silicon cantilever with a spring constant of 2 N/m and a resonance frequency of 70 kHz. The same tip was used for domain imaging in the piezoresponse mode by applying a 9.2 kHz, 10 V (peak to peak) modulation voltage. All measurements were performed at ambient environment u
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