Samarium Nickel Oxides Uses & Benefits

The ocean electric field is an important feature of ocean physics. Collecting electric field signals is of great significance for the study of subsea geological structures, water target detection, physical ocean and ocean physical properties. In order to collect and study ocean electric field signals, the research on ocean electric field sensors (electrodes for short) becomes particularly important. The principle of the electrode detection signal is to measure the potential difference between the two poles, and then obtain the weak electric field signal, and then obtain the target signal through the signal reduction, filtering, amplification and other external methods. The quality of the electrode directly determines the quality of the collected electric field signal.

The electrode materials currently used abroad are Pb/PbCl, Zn, carbon fiber, Aq/AgCl, Cu/CuSO, carbon aerogel, calomel, etc. In China, silver chloride, graphene, carbon fiber are mainly used. In the external research stage, seawater is corrosive and may have electrochemical reactions with the electrodes. Therefore, if the electrode material has poor corrosion resistance, the collected signals will be inaccurate, and the electric field signals are mostly medium and low frequency. The electrode needs to be placed in the ocean for a long time. In order to detect medium and low frequency signals, it generally needs to be placed in seawater for more than a week, which requires the electrode performance to be stable in seawater for a long time. At the same time, the amplitude of the electric field signal in the ocean is related to the distance. 

As the distance increases, the signal amplitude and noise will also increase. However, due to the limited operating conditions in the ocean, it is not easy to achieve a large sensor distance in the ocean, and the sensor distance is generally controlled within 100m. , so the electric field signal that can be measured is very weak, and the amplitude is as small as microvolt level. The signal may be attenuated on the surface of the electrode during propagation in seawater, and it is difficult for insensitive electrodes to accurately detect it. As the depth increases, the water pressure will increase, and if the sensor has poor pressure resistance, it will be difficult to work normally. 

In addition, the contact between the electrode and the seawater interface will have a contact cathode, which will generate thermal noise. If the contact resistance is too large, it will affect the measured electric field signal waveform and lead to misalignment. This requires the detection electrode to have the following properties: ①Strong stability: long-lasting When placed in seawater, it will not be corroded and can work upright. ②High measurement sensitivity: It needs to have high sensitivity to low-frequency signals, and the signal attenuation on the electrode surface is small. ③Strong pressure resistance: able to withstand water pressure. ④High signal-to-noise ratio: The target signal required to be acquired has low noise.

1. The principle of ocean electric field detection

The detection principle of the ocean electric field is to put the electrodes into the seawater, and use the spontaneous potential method to measure the potential difference between the two electrodes to obtain the electric field signal, which is similar to the principle of measuring the voltage across the resistor. First measure the voltage U between a pair of electrodes in one direction, and then measure the electrode spacing L, and calculate the field strength E=U/L in the study area. In the process of acquiring ocean electric field information, the electrode is the bridge connecting the seawater and the external circuit, as shown in Figure 1, R is the input impedance of the signal acquisition system.

Fig.1 Schematic diagram of marine electrodeconnection system

2. Samarium nickelate (SmNiO3) electric field sensor

Perovskite-type composite oxides are a new type of material in recent years with special electromagnetic and chemical properties. Such substances have peculiar structures and can be used in sensors, solid fuel cells and other fields, and have become a research hotspot in recent years.

The ampulla of Lorentz is the body hole that sharks use to detect weak electrical currents on the seafloor to find prey, as shown in Figure 2. Researchers at Purdue University in the United States imitated the ampulla of Lorentz and developed a new type of samarium nickelate electric field sensor, which can detect the weak electric field in the ocean, and will change color after detection. Stable work.

Fig.2 The ampullae Lorenzini of shark

Samarium nickelate is a quantum material that utilizes the interaction of quantum mechanics. Under the action of the ocean electric field, hydrogen ions enter the lattice of samarium nickelate and react with samarium nickelate to form samarium nickel hydride, which makes the 3D orbit of nickel atoms. The transition occurs, and the resistance characteristics are greatly reversed, and samarium nickelate changes from a metallic state to an insulating state, which is the process of metal-insulator phase transition. In essence, this phase transition is caused by the change of the chemical doping concentration of samarium nickelate, that is, the concentration of H+, caused by the action of the electric field. 

Research has shown that this process is reversible. Unlike some metals, such as aluminum, samarium nickelate immediately forms a dense oxide film in cold seawater that hinders electrochemical reactions. This material is not only not easily corroded in seawater, can maintain functional stability for a long time, can be recycled, and is highly sensitive to weak electric signals, which can realize high-precision measurement of ocean electric fields. It can be seen that samarium nickelate ocean electric field The sensor has certain advantages in detecting the weak electric field of the ocean and meets the aforementioned detection requirements. This research provides a new method for ocean electric field measurement.

3. Metal-insulator phase transition of rare earth nickelate RNiO3

The metal-insulator phase transition property of nickelates is the biggest difference between nickelates and perovskites. Metal-Insulator (MI) phase transition means that when the external conditions such as field intensity, light intensity, chemical doping concentration, temperature, and pressure are changed, due to the separation of overlapping energy bands, the nickelate changes from a metallic state to an insulating state. state, or the nickelate transitions from an insulating state to a metallic state due to the reduction of the gap between the valence and conduction bands, and the electromagnetic and optical properties of nickelates are greatly transformed due to the metal-insulator phase transition, As mentioned above, as a typical nickelate, samarium nickelate has the characteristics of metal-insulator phase transition. Under the action of an electric field, hydrogen ions enter the lattice of samarium nickelate and interact with samarium nickelate to form hydrogenation Samarium nickelate transforms the 3D orbital of nickel atoms, and samarium nickelate changes from a low-resistance metallic state to a high-resistance insulating state, and the color changes significantly, as shown in Figure 3. The essence of samarium nickelate metal-insulator phase transition is the Coulomb interaction between carriers at low temperature. This quantum effect allows samarium nickelate to be used in the field of ocean electric field detection.

Fig.3 Schematic diagram of the interactionprocess between hydrogen ionsand SmNiO3

4. Preparation method of samarium nickelate

At present, the methods for preparing samarium nickelate thin films include metal pulsed laser deposition, organic chemical vapor deposition, magnetron sputtering technology and sol-gel method in physical vapor deposition technology. Among them, pulsed laser deposition technology is the most widely used in domestic laboratories in recent years. Pulsed laser deposition is a preparation method that bombards a substance with a laser to obtain the desired thin film. 

Using laser bombardment of the target, the plasma obtained on the substrate forms a stable substate Ni3+ The target for preparing samarium nickelate is obtained by the all-solid-phase sintering method. On the issue of preparing samarium nickelate, it is different from metal organic chemical vapor deposition. The main advantage of the method compared with pulsed laser deposition is that the equipment is easy to use, but it is insufficient in the uniformity, area and cleanliness of the film formation. At the same time, the films prepared by pulsed laser deposition are prone to produce oxygen-containing defects, which may lead to the destruction of the metal-insulator transition.

5. Research status of samarium nickelate at home and abroad

1) Research on electrical properties

In 2016, in order to suppress the leakage of fuel cells, the Ramanathan team of Harvard University introduced samarium mirror acid to the field of solid oxide fuel cells for the first time. They found that protons can spontaneously incorporate into samarium nickelate at room temperature, making it metal. --Insulator phase transition, while protons can conduct fast in samarium nickelate. This indicates that samarium nickelate not only has good electrical insulating properties, but also has good proton conductivity. Therefore, they used the characteristic of samarium nickelate as an electrolyte for solid fuel cells to create a new type of fuel cell.

In 2018, a Purdue University team imitated the above-mentioned "ampulla of Lorentz" and developed a samarium nickelate electrode sensor. The voltages that such sensors can detect are on the order of the tiny voltages produced by marine organisms. The team calculated the detection distance of the sensor, which is about the detection distance of the weak electroreceptors of sharks.

The Purdue University researchers also experimented with doping samarium nickelate with lithium ions and lithium. They added lithium ions to samarium nickelate and found that this would lead to an increase in the conductivity of samarium nickelate and expansion of its crystal structure, as shown in Figure 4, they added lithium metal to samarium nickelate and found that nickel Samarium acid becomes an insulating state. Adding electrons to the material instead makes it more insulating.

Ramanathan's research team studied the regulation of the electric field on the phase transition temperature of the samarium acid film of dry mirror. The experiment showed that with the change of the applied forward bias, the electric anodic change of the samarium acid samarium acid did not change significantly, but when a negative voltage was applied, its resistance It should be lowered, but the experiment showed the opposite result. When a voltage of 1.2V was added, the resistance changed abnormally. They speculate that this phenomenon is not caused by the electrostatic field alone, but may be due to the electrochemical reaction of samarium nickelate with the ionic liquid.

In 2017, Sun Yan et al. of East China Normal University realized the electrostatic field regulation of the metal-insulator phase transition of samarium nickelate thin films based on the above research of Ramanathan's team using the electric double layer structure.

In 2018, Hu Haiyang of University of Science and Technology Beijing, etc., based on the preparation of samarium nickelate, used the lattice mismatch between samarium nickelate and the substrate to realize the control of the phase transition temperature of samarium nickelate and the regulation of its electronic orbital structure.

Fig.4 Schematic diagram of lithium doping in SmNiO3

2) Preparation related studies

In recent years, many domestic research teams have epitaxially grown samarium nickelate thin film materials on substrates (usually lanthanum aluminate, LaAlO3, etc.) by pulsed laser deposition, and obtained the most suitable preparation conditions through experiments.

The effect of strain relaxation on the structural stability of samarium nickelate thin films grown on epitaxially grown dry SrTiO3 substrates was studied at the Institut Nérol, France. The researchers verified that samarium nickelate can exist more stably on STO through high-resolution X-ray radiation. They discussed the quality of the film by simulating the XRD profile and X-ray reflectivity, and also achieved the stabilization of the samarium nickelate thin film. It was found through experiments that the relaxation of epitaxial strain would lead to the dissociation of the samarium nickelate phase into NiO and Sm2O3 .

3) Study of Optical Properties

In 2016, Yu Nanfang's research team discovered that samarium nickelate can achieve continuous control between opacity and transparency in the visible to mid-infrared spectrum through electrical tuning. After being doped with electrons, samarium nickelate becomes more insulating in electrical properties and more transparent in optical properties. By adjusting the electric field, the optical band barrier of samarium nickelate is changed, so that electrons cannot pass through but light can pass through, The process is also reversible, and the study is the first exploration of the optical properties of samarium nickelate.

Another team, through the first-principles of the optical properties of samarium nickelate and the study of intrinsic point defects, learned that oxygen vacancies increase the transmittance of visible light, while nickel vacancies decrease the transmittance of infrared and visible light.

6. Application prospects

The samarium nickelate electrode sensor can monitor the activities of unmanned underwater vehicles, ships, etc. by detecting the sub-volt potential in salt water, and is widely used in the marine field. Samarium nickelate can also be used as a pH sensor, a thermistor, and may also be used to promote research on new algorithms that mimic the human brain. It is the basis of brain-inspired computer materials containing artificial synapses.

In addition to its electrical application prospects, samarium nickelate has potential new functions for controlling thermal radiation to make smart infrared camouflage and thermoregulatory devices. At the same time, because the material can switch between transparent and opaque states at high speed, it can be used in free-space optical communication. In addition, this material can also be used to make "smart windows".

The above information is excerpted from "Research progress of samarium nickelate and its feasibility analysis for marine electric field sensors".