We observe a stringlike domain penetration from a ferroelectric surface deep into the crystal bulk induced by a high voltage atomic force microscope tip. The domains, which resemble channels of an electrical breakdown, nucleate under an electric field of around 10(7) V/cm at the ferroelectric surface, and grow throughout the crystal bulk where the external electric field is practically zero. A theory explaining the shape of the formed domains is presented. It shows that the driving force for the domain breakdown is the decrease of the total free energy of the system with increasing domain length.

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Mono-and periodically poled domain structures of ferroelectric KTiOPO 4 crystals have been studied by Kelvin probe force microscopy. This scanning probe method has allowed us to image the domain structure using a contact potential difference contrast between 180°ferroelectric domains. The measured contact potential difference between adjacent domains showed that the screening in the KTiOPO 4 crystals is provided by the highly mobile potassium ions. The screening charge density distribution and the resulting Debye length near the polar faces have been estimated.

Ferroelectric domains formed in the electric field of an atomic force microscope decay with time when the reversal voltage is removed. We propose a theory for this process. Dynamic equations describing the time evolution of the domain sizes are constructed and solved. It is shown that the larger the domains, the more stable they are. The time dependences of the domain length and base radius are qualitatively different. The radius of the domain decreases during the decay process, and for a large domain there is a plateau in its time dependence. In contrast to this, the length of the domain first does not decrease but rather grows significantly and then rapidly drops. We introduce the concept of critical radius for the domain stability. Only domains with a radius exceeding the critical radius have a long lifetime, which increases exponentially with the initial domain radius. The calculated value of the critical radius of stability in barium titanate is in reasonable agreement with the experiment. Possible means to stabilize the domains are proposed.

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