An oxygen sensor for detecting gas concentration based on either an electric current value or a resistance value measured when a voltage is applied to a sensor element includes gaps formed between electrodes arranged in an element main body and ridges where surfaces of an element touch each other. These gaps will be escaping parts for expansion and contraction of electrode material that accompany thermal expansion and contraction of a sensor main body, and concentration of thermal stress at edge parts of the element main body may thus be eliminated, thereby alleviating thermal stress on the oxygen sensor. This allows provision of a gas sensor that controls generation of cracks in the element and that is stably usable over a long period of time.

A gas sensor includes an electrochemical cell having a solid electrolyte layer disposed between a sensing electrode and a reference electrode; a heater disposed in thermal communication with the electrochemical cell, the heater having a positive heater lead and a negative heater lead; a reference gas channel; a reference chamber in fluid communication with the reference electrode; a pump cell having a first pump cell electrode in fluid communication with the reference gas channel and also having a second pump cell electrode in fluid communication with the reference chamber. The first pump cell electrode has a pump cell first lead which forms a first electrical junction with either the positive heater lead and the negative heater lead and the second pump cell electrode has a pump cell second lead which forms a second electrical junction with the same heater lead as the pump cell first lead.

An oriented apatite-type oxide ion conductor includes a composite oxide expressed as A.sub.9.33+x[T.sub.6.00yM.sub.y]O.sub.26.0+z, where A represents one or two or more elements selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Be, Mg, Ca, Sr, and Ba, T represents an element including Si or Ge or both, and M represents one or two or more elements selected from the group consisting of B, Ge, Zn, Sn, W, and Mo, and where x is from 1.00 to 1.00, y is from 0.40 to less than 1.00, and z is from 3.00 to 2.00.

The inequality Voff<Va<Vb is satisfied, assuming that Va is a first voltage applied to a preliminary oxygen concentration control unit at a time of a first operation thereof, Vb is a second voltage applied to the preliminary oxygen concentration control unit at a time of a second operation thereof, and Voff is a voltage applied thereto at a time when the preliminary oxygen concentration control unit is stopped.

Provided are a gas sensor element which is not prone to decreased precision of gas detection due to a decrease in temperature of a gas to be measured, and a gas sensor. An aspect of the present invention is a gas sensor element for detecting a specific gas included in a gas to be measured, the gas sensor element being provided with a solid electrolyte, a reference electrode, a measurement electrode, and a gas restricting layer. The thickness dimension WA of a portion of the gas restricting layer that is in contact with the measurement electrode, the thickness dimension WB of a portion of the gas restricting layer that is in contact with the solid electrolyte, and the thickness dimension WC of the measurement electrode satisfy the conditions WB>WA and WBWA>WC. In a gas sensor element provided with such a gas restricting layer, the heat capacity of the gas restricting layer can be increased without hindering the gas to be measured from reaching the measurement electrode. Through this gas sensor element, the amount of change in temperature of the gas sensor element can be reduced and a decrease in gas detection precision can be mitigated even when the temperature of the gas to be measured is reduced.

An improvement in the method or technique of conditioning a gas sensor is provided through the application of Pulse Discharge Technique (PDT) in order to condition mixed-potential gas sensors. A modified planar sensor design to minimize sodium atom diffusion and platinum electrode poisoning under conditions of PDT are provided. Modification of the PDT hardware is provided without modification of the sensor design. The improvement method comprises: a) Replace a single polarity power supply with a power supply with floating positive and negative output; b) Connect one of the heater leads with the reference electrode lead and connect it to the ground.

A gas sensor capable of measuring a high concentration range is provided. A sensing electrode provided in a sensor element of a mixed-potential gas sensor for measuring the concentration of a predetermined component in a measurement gas is formed of a cermet including a noble metal and an oxygen-ion conductive solid electrolyte. The noble metal includes Pt and Au. A Au abundance ratio, which is an area ratio of a portion covered with Au to a portion at which Pt is exposed in a surface of noble metal particles forming the sensing electrode, is 0.1 or more and less than 0.3.

Apparatus and associated fabrication methods related to a micro-electro-mechanical system (MEMS) based electrochemical sensor include an electrolyte contacting two or more electrode(s) arranged on a substrate, and a high surface area electrode disposed on top of at least a sensing electrode of the sensor. Various embodiments of the high surface area electrode may increase a current or potential produced by the MEMS-based electrochemical sensor in response to one or more targeted chemical species or gases, and allow fabrication and operation of smaller electrochemical sensors. The electrodes may be electrically coupled to control and measurement circuitry. In some examples, the control and measurement circuitry may be formed on the same substrate.

An A/F sensor includes a solid electrolyte body and a heater. The A/F sensor is disposed downstream of a purification device in a flow of exhaust gas g. The purification device purifies the exhaust gas g. The solid electrolyte body is in a cup shape. The solid electrolyte body has an outer surface provided with a measurement electrode 4 contacting the exhaust gas g, and an inner surface provided with a reference electrode contacting reference gas. The solid electrolyte body is made of zirconia. The solid electrolyte body includes a detection part sandwiched between the measurement electrode and the reference electrode and conducted with oxygen ions. The detection part has a cubic phase ratio of 88 mol % or more.

A gas sensor element having good sensitivity and responsiveness at low temperature, and a gas sensor are provided. The gas sensor element includes a solid electrolyte member made of an oxygen ion conductive ZrO.sub.2-based ceramic, and a reference gas-side electrode and a measuring gas-side electrode respectively provided on a surface and the other surface of the solid electrolyte member. The gas sensor includes the gas sensor element. The reference gas-side electrode and the measuring gas-side electrode are formed so as to face each other with the solid electrolyte member interposed therebetween, and are both made of a noble metal or a noble metal alloy. A mixed layer with an average thickness of 800 nm or less is formed between the solid electrolyte member and the reference gas-side electrode. The mixed layer contains a noble metal or a noble metal alloy and a ZrO.sub.2-based ceramic mixed with each other.