Thesis (Ph. D.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains xi, 125 p. : ill. (some col.) Includes abstract. Includes bibliographical references (p. 121-125).

The Ta-modified niobate lithium [LiNb1-xTaxO3, abbreviated to LNT] thin films were deposited on Pt/Ti/SiO2/Si substrates by spin coating with sol-gel technology and rapid thermal processing in this thesis. 1,3 propanediol was used as solvent to minimize the number of cycles of spin coating and drying processes to obtain the desired thickness of thin film. By changing the Ta content (x=0~1), the effects of various processing parameters on the thin films growth are studied. The effects of various Ta content on the response of pyroelectric IR detector devices are studied also. Experimental results reveal that the Ta content will influence strongly on grain size, dielectricity, ferroelectricity and pyroelectricity of LNT thin films. With the increase of Ta content, the grain size of LNT thin film decreases slightly, and highly c-axis orientated LNT films have been obtained for x=0.2. With the increase of Ta content, The relative dielectric constant of LNT thin film increases from 33 up to 62. The dielectric loss (tand) increases from 0.00374 to 0.00686,Coercive Field (Ec) decreases from 81.09KV/cm to 32.07KV/cm, and Remanent polarization (Pr) decreases from 8.48 mC/cm2 to 2.2 mC/cm2, pyroelctric coefficient (g) increases from 2.76´10-8 C/cm2K up to 4.51´10-8 C/cm2K with an increase of Ta content. In addition, the results also show that the LNT thin film possesses the largest figures of merit Fv (2.66¡Ñ10-10 Ccm/J) and Fm (2.57¡Ñ10-8 Ccm/J) at the heating temperature of 700¢J and Ta content of 20mol%. The voltage responsivities (Rv) measured at 70 Hz has a largest value of 7020 V/W with the Ta content of 20mol%. The specific detectivity (D*) measured at 200 Hz has the maximum value of 7.76¡Ñ107 cmHz1/2/W with the Ta content of 20mol%. The results show that LNT(20) pyroelectric thin film detector exists both the maximums of voltage responsivity and specific detecivity. Therefore, optimizing the conditions of this study, LNT(20) thin film will be the most suitable for IR detector application.

Ferroic materials play an increasingly important role in novel (nano-)electronic applications. Recently, research on domain walls (DWs) received a big boost by the discovery of DW conductivity in bismuth ferrite (BiFeO3 ) and lead zirconate titanate (Pb(Zrx Ti1−x )O3) ferroic thin films. These achievements open a realistic and unique perspective to reproducibly engineer conductive paths and nanocontacts of sub-nanometer dimensions into wide-bandgap materials. The possibility to control and induce conductive DWs in insulating templates is a key step towards future innovative nanoelectronic devices [1]. This work focuses on the investigation of the charge transport along conductive DWs in ferroelectric single crystals. In the first part, the photo-induced electronic DC and AC charge transport along such DWs in lithium niobate (LNO) single crystals is examined. The DC conductivity of the bulk and DWs is investigated locally using piezoresponse force microscopy (PFM) and conductive AFM (c-AFM). It is shown that super-bandgap illumination (λ ≤ 310 nm) in combination with (partially) charged 180° DWs increases the DC conductivity of the DWs up to three orders of magnitude compared to the bulk. The DW conductivity is proportional to the charge of the DW given by its inclination angle α with respect to the polar axis. The latter can be increased by doping the crystal with magnesium (0 to 7 mol %) or reduced by sample annealing. The AC conductivity is investigated locally utilizing nanoimpedance microscopy (NIM) and macroscopic impedance measurements. Again, super-bandgap illumination increases the AC conductivity of the DWs. Frequency-dependent measurements are performed to determine an equivalent circuit describing the domains and DWs in a model system. The mixed conduction model for hopping transport in LNO is used to analyze the frequency-dependent complex permittivity. Both, the AC and DC results are then used to establish a model describing the transport along the conductive DW through the insulating domain matrix material. In the last part, the knowledge obtained for LNO is applied to study DWs in lithium tantalate (LTO), barium titanate (BTO) and barium calcium titanate (BCT) single crystals. Under super-bandgap illumination, conductive DWs are found in LTO and BCT as well, whereas a domain-specific conductivity is observed in BTO.