The present cumulative thesis discusses the challenging and exciting way to utilize the outstanding physical properties of functional oxide materials for the development of new applications and devices, with a focus on the integration of lead-free ferroelectric thin films into bioelectronics. The cumulative thesis comprises four publications - Publication I - IV - and is organized as follows. The first part (Publication I + II) is devoted to the pulsed laser deposition (PLD) of lead-free 0.5(Ba0:7Ca0:3)TiO3-0.5Ba(Zr0:2Ti0:8)O3 (BCZT) ferroelectric thin films on different substrates and their detailed electrical characterization and analysis by impedance spectroscopy. For the deconvolution of measured impedance spectra by equivalent-circuit fitting, a new equivalentcircuit element based on the theory of interface pinning in random systems - the domain wall pinning element - is introduced which models the impedance of a ferroelectric including the contribution from domain-wall-motion in the subswitching regime. This approach is applied to impedance spectra collected on polycrystalline and epitaxial BCZT thin film capacitor stacks, and the domain-wall-motion induced field- and frequency-dependent dielectric response of the BCZT films is extracted by domain wall pinning element modeling and equivalent-circuit fitting. Moreover, an extended Rayleigh analysis is presented which allows one to quantify the coupling strength between dielectric nonlinearity and frequency dispersion and the identification of different domain-wall-motion regimes in the BCZT films. The corresponding domain-wall dynamics in the BCZT thin films is discussed in detail and a schematic diagram of the different domain-wall-motion regimes is presented. The results from the extended Rayleigh analysis - obtained on epitaxial and polycrystalline BCZT films - indicate, that the presence of grain boundaries in BCZT reduces the coupling strength between dielectric nonlinearity and frequency dispersion and suppresses the motion of internal domain-wall segments in addition to the suppression of the irreversible center-of-mass motion of the domain walls. In the second part (Publication III), microelectrodes based on conductive sputtered IrO2 films (SIROFs) - which are utilized to provide electro-neural interfaces for subretinal stimulation in the state-of-the-art retinal prosthesis “Retina Implant Alpha AMS” - are analyzed in detail by electrochemical impedance spectroscopy (EIS) and subsequent equivalent-circuit analysis. The supercapacitive behavior of the investigated SIROF-microelectrodes is modeled by a pseudocapacitance Cp in parallel to the capacitance of the electrochemical double layer CDL, and both capacitances are represented by a constant phase element (CPE) in the equivalent-circuit model. By fitting the measured EIS data with the equivalent-circuit model, Cp and CDL are quantified from the obtained CPE fit parameters, and the resulting supercapacitive behavior is in agreement with cyclic voltammetry measurements. The results indicate, that the pseudocapacitance Cp due to quasi-continuous reversible reduction and oxidation between Ir3+/ Ir4+ valence states is the dominant contribution to the supercapacitance and to the charge injection capacity (CIC) of the investigated SIROF-microelectrodes. Finally, in the third part (Publication IV), a new approach for bioelectronic interfacing of electrogenic cells or tissue is introduced, which utilizes a conductive microelectrode coated with an insulating ferroelectric layer for extracellular electrical stimulation. It is shown, that the ferroelectric polarization current contributes to the extracellular stimulation current provided by the ferroelectric microelectrode. The switching regime of a ferroelectric microelectrode in an electrolyte-ferroelectric-conductor configuration is analyzed based on the traditional Kolmogorov-Avrami-Ishibashi (KAI)-model and the time-dependent stimulation current in response to an applied voltage step is simulated for a generic microelectrode geometry. It is shown that, depending on the remanent polarization Pr of the utilized ferroelectric, the polarization current in the switching regime can increase the CIC by up to two orders of magnitude as compared to the commonly used extracellular capacitive stimulation with microelectrodes coated with an insulating dielectric layer. The results pave the way for extracellular electrical stimulation with small microelectrodes (30 um in diameter) without toxic electrochemical effects, which is crucial for implantable neuroprosthetic devices such as high-resolution retinal-implants or brain-machine interfaces.