Effects of electrochemical hydrogen charging on lead-based relaxor ferroelectric multilayer ceramic capacitors
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Effects of electrochemical hydrogen charging on lead-based relaxor ferroelectric multilayer ceramic capacitors Wanping Chen, Longtu Li, Yu Wang, and Zhilun Gui Department of Materials Science and Engineering, Tsinghua University, Beijing 100084, China (Received 24 March 1997; accepted 17 October 1997)
Lead-based relaxor ferroelectric multilayer ceramic capacitors (MLC’s) were placed in 0.05 M NaOH solution to evolve hydrogen on their silver termination electrode by electrolysis of water. After this treatment, the MLC’s failed as their insulation resistance was greatly decreased, their dielectric loss was considerably increased, and their capacitance was obviously decreased. By annealing in air at 650 ±C for 30 min, the properties of the MLC’s were restored. It is proposed that electrochemically generated hydrogen atoms can diffuse into the ceramic body of MLC’s and undergo reduction to it, which may be one of the reasons for the negative influence of electroplating on lead-based relaxor ferroelectric MLC’s.
Multilayer ceramic capacitors (MLC’s) are used widely in various electronic equipment. During the fabrication of those MLC’s intended for use in surface mounting, nickel is plated as a barrier layer to prevent the dissolution of silver from the termination electrode into solder, and tin is plated to improve the solderability. The electrical properties of MLC’s are often influenced adversely during the electroplating.1 For those MLC’s made of lead-based relaxor ferroelectrics, which are very attractive for their high dielectric constants, broad dielectric maxima, and relatively low firing temperatures,2,3 the influence of electroplating is sometimes so serious that it hinders their use in surface mounting. Though the influence of electroplating can be very serious and obvious, its cause is still not clear. Much attention is paid to the permeation of plating solutions in the ceramic body of MLC’s,4 while the influence of the electroplating process is usually neglected. As water is the base of most electrolytes, hydrogen deposition is common in electroplating. Hydrogen not only has a decisive influence on electrodeposits, but also reacts with the base materials.5 The electrical properties of the base materials could be affected greatly by the reaction of hydrogen.6 Therefore, attention should also be paid to the possible influence of hydrogen generated in the electroplating process. Electrochemical hydrogen charging procedure, called “the poor man’s ion implantation method” by Dr. Christoph J. Raub,5 is frequently used to study the behavior of hydrogen in various materials,7 in which the substrate material is made a cathode in a dilute acidic solution or a dilute alkaline solution to evolve hydrogen. In this paper this experimental method was applied to examine the possible influence of hydrogen on lead-based relaxor ferroelectric MLC’s. Some 0805 MLC samples (manufactured by Fenghua Company, Guangdong Province, China) of the 1110
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