Effect of the electrical boundary condition at the crack face on the mode I energy release rate in piezoelectric ceramics Appl. Phys. Lett. 94, 081902 (2009); 10.1063/1.3088855Double torsion testing and finite element analysis for determining the electric fracture properties of piezoelectric ceramics Influence of temperature on the electromechanical and fatigue behavior of piezoelectric ceramics Crack propagation in a piezoelectric lead-zirconium-titanate ͑PZT͒ material under simultaneous mechanical loading and applied electric fields is studied using the Vickers indentation technique. It is demonstrated experimentally that electric fields can inhibit or enhance crack propagation in piezoelectric materials. Cracks introduced by indentation are observed to propagate less under a positive applied electric field ͑the polarity of the field was the same as that for poling͒, whereas under a negative applied electric field, crack propagation is enhanced. Such an effect is observed to be more profound with increasing electric-field strength and decreasing mechanical loading. Attempts are made to compare these experimental observations with the results of various theoretical analyses. A mechanism for the change in crack propagation behavior of the piezoelectric PZT material under applied electric fields is presented.

Cubic boron nitride (c-BN) thin films are of significant interest because of their diamond like structure and properties. c-BN shows high thermal conductivity, chemical inertness against ferrous metals even at high temperatures, wide band gap, and good transmittance over a wide spectral range from UV to visible. Applications of c-BN include hard protective coatings for cutting tools, in optical instruments as UV detectors, as emitters, and in high temperature electronic devices. However, synthesis of phase pure c-BN thin films continues to be very challenging. The present study reviews the current status of the synthesis, characterisation, mechanical, electrical, and optical properties of c-BN thin films. Both physical and chemical vapour deposition methods used for the preparation of the c-BN films are covered. In addition, different nucleation and growth models of c-BN formation and growth on different substrates are described. The influence of process parameters such as ion energy, growth temperatures, chemical precursors, bias, and impurities on the nucleation and growth is reviewed. Mechanical properties including hardness, elastic modulus, and stiffness of c-BN films are discussed. The latest developments in electrical properties of the c-BN films based on metal-insulatorsemiconductor (MIS) hetero-structures, interface states, impurity states, conduction mechanism, field emission properties, and negative electron affinity (NEA) are presented. The optical properties and cathodoluminescence characteristics of BN films are also discussed.

Diamond thin films have outstanding optical, electrical, mechanical and thermal properties, which make these attractive for applications in a variety of current and future systems. In particular, the wide band gap, optical transparency and unusually high thermal conductivity of diamond thin films make them an ideal semiconductor for applications in current and future electronics. However, synthesis of diamond thin films with adequate quality remains a challenging task. Synthesis of diamond at low temperatures is even more challenging because of the difficulties in the nucleation and growth steps involved in diamond thin film deposition on a variety of substrates. Among the several deposition techniques for synthesising diamond films, plasma enhanced chemical vapour deposition is the most promising technique because of its potential for low temperature synthesis. Consequently, the first part of this paper reviews the current state of the nucleation and growth of diamond during chemical vapour deposition. A uniform and high nucleation density is a prerequisite for getting a good quality diamond film with significant growth rate. Also, since the process conditions for nucleation and growth steps are different, attempts are made in this review to identify the important parameters responsible for enhancing the nucleation and growth rates of diamond film. Describing the indispensable need for low temperature growth of diamond film, the second part of the paper reviews the research on the growth of diamond thin films at low temperatures. In spite of the slower kinetics at lower deposition temperatures, an attempt is made to identify the key processing conditions, which enhance the low temperature growth process. In addition, the mechanisms of diamond nucleation and growth are discussed based on the observations from in situ characterisation techniques such as Fourier transform infrared reflection absorption spectroscopy, real time spectroscopic ellipsometry and molecular beam mass spectroscopy.

No abstract

No abstract