Ferroelectric single-crystal nano-rods grown within a nano-porous aluminum oxide matrix

Growing ferroelectric nano single-crystals with uniform polar direction in-vertical to the substrate plane is of high scientific and technological interest for understanding ferroelectric behavior in small dimensions and developing future devices. Single-crystals of Rochelle Salt (RS) and potassium nitrate (PN), with preferred orientation, were grown inside a highly-dense array of aluminum oxide nano-pores, oriented in-vertical to the substrate plane. Preferred orientation was also obtained for potassium niobate crystals. Under certain conditions, nucleation occurred only at the pore bottom due to a tight control over temperature, liquid composition, and pore size. Nucleation at the bottom is necessary for the formation of identically-aligned single-crystals within the pores. Non-linear dielectric behavior was observed in the case of RS and PN crystals inside the pore. The pores stabilize the ferroelectric phase of RS up to 30A degrees C above the upper Curie temperature of bulk (24A degrees C). In the case of PN-filled pores, the crystals grow in the non-ferroelectric orthorhombic phase. Upon applying an electric field of 200 kV/cm, a transition to the ferroelectric phase occurs, and a hysteresis loop appears. This phenomenon was not observed in bulk PN and is attributed to the effect of the hydrostatic pressure applied by the pore walls combined with the applied electric field.