| Memristor is a fundamental circuit element, which keeps a memory of itsresistance over time. Recently, circuit theory, electronic devices and materials related tomemristor are attracting more and more attention from researchers. In this paper, newmaterials for construction of bulk memristors have been prepared, meanwhile,investigations on the corresponding memristive behaviors and mechanism have beencarried out.Memristive behaviors, and the corresponding mechanism, have been found inAg|AgI|Ag sandwich structure. The γ-AgI nano-particles were prepared throughreactions in solutions, after which the nano-powders were pressed into bulk memristors.It’s found from the electrical test that the samples showed typical hystereticcurrent-voltage (I-V) characteristics and memristive behaviors, under the loading oftriangular wave voltage. Area of the I-V loop was found to shrink with increase involtage frequency, showing a resistance ratio between high resistance and lowresistance of over100. The switching voltage was measured to increase linearly withtesting voltage range, while decline with temperature increase. Additionally, resistancevalue of the low resistance state was also detected to decrease with temperature. The I-Vand resistance-voltage (R-V) plots under the loading of unidirectional and asymmetricvoltage scan were obtained. It’s revealed that memristive behaviors of AgI bulkmemristor originates from electro-redox reactions of I-at interface between Agelectrode and AgI electrolyte. Moreover, the resistance value of low resistance state isbelieved to depend on reaction speed at the interface, while the resistance value of highresistance state is controlled by the diffusion speed of supplying reactants.Investigation has been taken on the memristive I-V loop, resistance switching andmemristive mechanism of AgI|CoO|Ag bulk structure. Bulk memristor was constructedfrom CoO ceramic using a traditional solid reaction method in argon atmosphere.Electrical measurements were applied to investigate circuit properties of samples.Current in the sample and area of I-V loop were measured to decrease with increasingvoltage scan speed, and sample resistance was found to decrease with improvement inboth voltage and temperature. A set of current-controlled memristor state equations were provided, considering the relationship between resistance of negative coefficientthermistor and temperature, which successfully explained the memristive behaviors ofCoO ceramics. Joule heat is believed to improve the sample temperature and decreaseits resistance, while heat dissipation between sample and environment would decreasethe temperature and cause resistance increase. Resistance ratio of an ideal CoOmemristor was calculated to be over30000. The as-proposed memristive mechanismwas found to apply for other negative temperature coefficient thermistor basedmemristors, which was confirmed by results from as-prepared NiO and Co3O4ceramicsamples.Memristive behaviors were found for the first time in ZMFO polycrystallineceramics, memristive mechanism of which were analyzed. ZMFO samples wereobtained by solid reactions at high temperature. Electrons transportation properties ofAg|ZMFO|Ag bulk structure have been investigated. Memristive resistance switchingand hysteretic I-V characteristics were found in ZMFO bulk ceramic structure under theloading of triangular wave voltage. Good time retention was detected in resistance ofthe as-obtained sample, which was tunable by both electric field and magnetic field.Results form alternating current impedance measurements and hysteretic I-V loops fromdifferent temperatures confirm that the modulation of current on direction of atomicmagnetic moment, together with magnetic hysteresis effect of ferrite ceramics are bothresponsible for the memristive mechanism in ZMFO ceramics. Experiments operated onthe as-obtained magneto plumbite type strontium ferrite bulk ceramic sample illustratesthat the as-proposed mechanism is applicable for other ferrite ceramics bulk memristor. |
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