electrical resistivity
Enable an agent to identify electrical resistivity, assess whether a reported value applies to a material and operating condition, and decide whether it can support comparison, calculation or material selection.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
Researched by: Codex + Grok
Purpose and description
Enable an agent to identify electrical resistivity, assess whether a reported value applies to a material and operating condition, and decide whether it can support comparison, calculation or material selection.
Electrical resistivity is the intensive constitutive property of a material that relates electric field strength to current density (ρ = E/J in isotropic linear media), equivalently the DC resistance of a uniform prism multiplied by cross-sectional area and divided by length, with SI unit ohm-metre.
It can be Normalize reported resistivity units while retaining the original value and conditions.; Compare materials only after checking temperature, direction, material condition and measurement basis.; Infer resistivity from resistance and specimen geometry when the current-flow assumptions are justified.; Estimate specimen resistance from applicable resistivity and geometry.; Identify whether a discrepant value calls for contact checks, thermal stabilization, directional measurement or new material characterization.; Accept, qualify or reject a resistivity value for a stated design or analysis task..
Distinguishing features
A bulk resistivity value has units of ohm metre; a value in ohms describes resistance and requires geometry before it can establish resistivity.
For a homogeneous specimen with uniform current flow, resistance changes with length and cross-sectional area while the inferred resistivity should remain consistent at the same material state.
A sheet resistance in ohms per square requires a justified conducting thickness and suitable film assumptions before conversion to bulk resistivity.
Electrical conductivity is the reciprocal of scalar resistivity in the applicable linear description; directional tensor descriptions require matrix inversion rather than elementwise reciprocals.
A voltage drop dominated by electrodes or contacts cannot be assigned to bulk resistivity without separating those contributions.
Scope
+ Bulk electrical resistivity attributed to an identified material and material state
+ Scalar or tensor representation and the directions to which values apply
+ Dependence on temperature, composition, microstructure and electrical excitation
+ Measurement-derived values, uncertainty and separation of specimen geometry from material response
+ Conditions under which resistivity supports comparisons or resistance calculations
- Resistance of a complete component, circuit or installation
- Contact resistance and interface-specific resistivity as independently modelled quantities
- Sheet resistance as a distinct thin-film quantity
- Dielectric permittivity, polarization and breakdown strength
- Thermal resistivity and resistance to heat flow
- Complete impedance spectra and equivalent-circuit models
Characteristics
- Resistivity value
- Ω·m, with uncertainty or a qualified upper or lower bound Quantifies the material response and distinguishes an estimate from a measurement limit.
- Representation
- Scalar; directional value; tensor; effective value Determines whether a single number adequately describes the intended current direction and material structure.
- Material and specimen attribution
- Identified material, grade, batch, specimen and relevant preparation history Prevents values from being transferred between materially different compositions or structures.
- Temperature
- K or °C, with measurement location and stability where relevant Resistivity comparisons and predictions require a known thermal condition.
- Electrical excitation
- Current density in A/m² or electric field in V/m; frequency in Hz and waveform where applicable Exposes nonlinear response, frequency dependence and possible heating during measurement.
- Direction and coordinate frame
- Current and field directions relative to specimen axes, crystal axes or processing orientation Makes directional and tensor values interpretable.
- Material condition
- Relevant phase, moisture condition, strain, porosity, defect state and aging condition Identifies changes that may invalidate an otherwise correctly attributed value.
- Measurement basis
- Direct specimen measurement; geometry-based inference; fitted estimate; literature value; calculated prediction Determines what evidence and assumptions must accompany the value.
- Applicable regime
- Established temperature, excitation, frequency, direction and material-state limits Constrains reuse of the value outside the conditions that support it.
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 5 bundles · 9 layers · 16 findings · 30 questions.
Quantity identity Establishes which electrical material response the reported quantity represents.
Resistivity is readily confused with resistance, sheet resistance and contact effects, which support different decisions.
Bulk quantity boundary
Separates material resistivity from specimen and interface quantities.
Reported quantity identification
Record the quantity actually reported and the evidence for interpreting it as bulk electrical resistivity.
- Does the source report bulk resistivity, resistance, sheet resistance or an interface-specific quantity? definition
- Do the units and measurement description support the claimed quantity without an unstated thickness or geometry conversion? boundary
Constitutive representation
Determines how electric field and current density are related in the intended description.
Scalar, directional or tensor response
Record whether resistivity is a scalar, a directional observation or a tensor, with its defining convention.
- Is a scalar relation between electric field and current density justified, or must directional coupling be retained? definition
- Which coordinate frame and field or current directions define the reported components? measurement
- If the response is nonlinear or frequency dependent, what precise apparent, differential or complex quantity is being called resistivity? boundary
Material and condition Anchors resistivity to the material identity and physical conditions that make it applicable.
A resistivity value cannot be safely treated as a universal constant of a material name.
Material attribution
Identifies the material and structure represented by the value.
Composition and structure
Record composition, processing and structural details relevant to electrical transport.
- Which material grade, composition, dopant condition or batch does the value describe? provenance
- Which features such as crystallographic texture, porosity, phase mixture or processing direction must match before this value can be transferred? boundary
Operating condition
Records thermal, environmental and excitation conditions during characterization and use.
Condition-dependent value
Associate each value with the conditions under which it was established.
- At what specimen temperature, electrical excitation and frequency was the value established? measurement
- Were moisture, pressure, strain, illumination or magnetic field controlled where they could affect this material? measurement
- Which differences between characterization conditions and intended use require a correction or a new measurement? action
Measurement and inference Establishes how observations support the resistivity value and its uncertainty.
Geometry, current distribution and unwanted voltage or current paths can make an apparent resistivity unrepresentative of the bulk material.
Specimen to property
Captures the measurement arrangement and conversion from electrical observations to material response.
Method and geometric assumptions
Record the method, specimen dimensions and current-flow assumptions used to derive resistivity.
- Which method and electrode arrangement produced the current and voltage observations? provenance
- Which dimensions, thicknesses or geometry correction factors enter the resistivity calculation? measurement
- What supports the assumed current distribution, homogeneity and directional interpretation for this specimen? boundary
Measurement limitations
Identifies unwanted contributions and the limits of the resulting estimate.
Bulk signal and uncertainty
Record how the bulk response was distinguished from contacts, leakage, offsets and instrument limits.
- How were contact voltage drops, leakage paths, thermoelectric offsets and specimen self-heating assessed or controlled? measurement
- What uncertainty follows from the electrical readings, dimensions, temperature and method corrections? measurement
- Does the evidence support a numerical value, a detection-limited bound or a requirement to repeat the measurement? action
Applicability and decisions Defines how resistivity evidence may support calculations, comparisons and follow-up actions.
An agent must know when a recorded value remains usable and when extrapolation or conversion would exceed its evidence.
Comparison and conversion
Constrains normalization, conductivity conversion and geometry-based calculations.
Permitted derived uses
Identify which comparisons and derived quantities are justified by the recorded representation and conditions.
- Are the material conditions, temperatures, directions and excitation regimes sufficiently aligned for the proposed comparison? boundary
- Does a proposed conductivity conversion require a scalar reciprocal or inversion of a complete resistivity tensor? action
- Does the intended resistance calculation justify a uniform geometric relation, or require a spatial current-flow model? action
Validity and recharacterization
Defines the evidence limits and changes that trigger review.
Use envelope and review triggers
Record supported operating ranges, decision criteria and reasons to obtain new evidence.
- Over what temperature, excitation, frequency and material-state range is the value or fitted relationship supported? boundary
- What application-specific criterion determines whether the value and its uncertainty are adequate for the intended decision? action
- Which changes in processing, aging, moisture, phase or measured response require recharacterization? action
Evidence and external alignment What the world already says about this thing, gathered so the model can be checked against it.
A model that cannot be lined up against existing standards, identifiers and practice cannot be adopted by anyone who already uses them.
Reported evidence
Findings from the breadth pass, kept separate from the structural claims.
Kinds and varieties
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Volume (bulk) DC resistivity of a homogeneous solid or liquid
- Surface resistivity of a planar solid (current constrained to a surface layer)
- AC and complex resistivity, including frequency-dependent and imaginary parts in dielectrics and dispersive earth
- Apparent resistivity as inverted from a geoelectrical electrode array
- Residual resistivity of a metal after phonon scattering is frozen out at low temperature
- Anisotropic (tensor) resistivity in crystals, composites, rolled metals and stratified ground
- Ionic or electrolytic resistivity of electrolytes, moist soils and mixed conductors
- Effective earth or soil resistivity as a field-scale equivalent used in earthing design
- Which of these kinds and varieties hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Identifiers and schemes
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Wikidata - Q179918 - Item for electrical resistivity as a physical quantity.
- IEC Electropedia / IEV - 121-12-04 - Quantity 'resistivity' in IEC 60050-121; conductivity is the neighbouring IEV entry.
- ISO 80000-6 - quantity name resistivity, symbol ρ, unit Ω·m - Quantities and units - Electromagnetism; item number varies by edition, so the quantity name is the stable handle.
- SI derived unit - Ω·m (ohm-metre) - Coherent SI unit; still often written ohm-cm or µΩ·cm in metals and soils practice.
- IACS - 100% IACS ≡ 1.7241×10⁻⁸ Ω·m at 20 °C - International Annealed Copper Standard; conductor materials are often named by % IACS rather than SI resistivity.
- Which of these identifiers and schemes hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Standards and regulation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- IEC 62631-3-1 (and legacy IEC 60093) - volume resistivity of solid insulating materials (IEC)
- IEC 62631-3-2 - surface resistance and surface resistivity of solid insulating materials (IEC)
- IEC 61340 series - electrostatics; classification of planar materials by surface resistivity for ESD control (IEC)
- ASTM D257 - DC resistance or conductance of insulating materials (ASTM International)
- ASTM B193 - resistivity of electrical conductor materials (ASTM International)
- ASTM G57 / ASTM G187 - field and laboratory soil resistivity for corrosion work (ASTM International)
- IEEE Std 81 - earth resistivity and grounding-system measurements (IEEE)
- ISO 1853 - resistivity of conducting and dissipative rubbers (ISO)
- ISO 3915 - conductivity/resistivity of plastics (ISO)
- Which of these standards and regulation hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Real-world use
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Specifying copper, aluminium and steel conductors and busbars (often as % IACS or µΩ·cm at 20 °C).
- Sizing and siting earth electrodes and substation grounding grids from measured soil resistivity profiles.
- Classifying ESD-protective packaging and flooring as conductive, dissipative or insulative by surface resistivity decades.
- In-line process control of semiconductor wafers and thin films with four-point probes (reported as resistivity or sheet resistance).
- DC and induced-polarisation geophysical surveys for minerals, groundwater and contamination, reported as apparent resistivity.
- Ranking soil corrosivity for buried pipe, tank and anode design.
- Condition assessment of cable and bushing insulation via volume resistivity or insulation resistance scaled to geometry.
- Water and ultrapure-water monitoring, usually as conductivity, which is the reciprocal of resistivity (MΩ·cm in UPW).
- Which of these real-world use hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Typical measurements
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Volume resistivity of metallic conductors at 20 °C - 1.6×10⁻⁸ (silver/copper) to about 1×10⁻⁶ (cast irons, some alloys) - Ω·m
- Volume resistivity of semiconductors - roughly 10⁻⁵ (heavily doped) to 10⁴ (near-intrinsic Si/Ge class materials) - Ω·m
- Volume resistivity of solid electrical insulation - 10⁸ to 10¹⁶ and higher when dry; collapses orders of magnitude with moisture - Ω·m
- Surface resistivity (ESD and insulation practice) - about 10³-10⁵ conductive, 10⁵-10¹² dissipative, >10¹² insulative (IEC 61340 decades) - Ω (often styled Ω/sq)
- Effective soil / earth resistivity - about 1 (wet clay, saline) to >10 000 (dry sand, crystalline rock); seawater ~0.2 - Ω·m
- Temperature coefficient of resistivity of pure metals near 20 °C - about 0.003-0.006 - K⁻¹
- Residual resistivity ratio (RRR) of pure metals - tens to >1000 for high-purity copper or aluminium - dimensionless
- Which of these typical measurements hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Failure modes and hazards
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Metal resistivity rises with temperature, increasing I²R heating and, in overloaded conductors, thermal runaway and fire.
- Moisture, ionic contamination or tracking can drop insulation volume or surface resistivity by many decades and precipitate dielectric breakdown or shock.
- Two-terminal readings fold in contact and lead resistance, so a measured 'resistivity' can be far above the true bulk value.
- A single scalar ρ is unrepresentative for anisotropic, layered, porous or skin-effect-limited bodies; designs then under- or over-estimate current paths.
- Seasonal drying or freezing can raise soil resistivity and leave an earth electrode with much higher resistance than the design measurement.
- High-resistivity ground increases touch and step voltages around faults; low-resistivity saline ground accelerates corrosion of buried metal.
- In thin-film interconnects, high current density in a low-resistivity metal still drives electromigration open circuits.
- Which of these failure modes and hazards hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Regional variation
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- SI and IEC work uses ohm-metre; US corrosion, soils and some wire tables still quote ohm-centimetre (factor of 100) or circular-mil-ohm per foot.
- Conductor trade practice names material by % IACS conductivity rather than SI resistivity, especially in North America.
- Surface resistivity is reported as ohms or as ohms per square depending on lab tradition; the numerical value is the same for a square specimen but the unit style differs.
- Earthing measurement practice follows IEEE Std 81 in much of North America and IEC/BS earthing guides (for example BS 7430) in the UK and many IEC markets.
- Ultrapure-water users speak in MΩ·cm resistivity; most other process industries speak in µS/cm conductivity of the same quantity.
- Geophysicists report apparent resistivity tied to a named array (Wenner, Schlumberger, dipole-dipole); materials labs report a geometry-corrected bulk ρ.
- Which of these regional variation hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Neighbouring kinds and how to tell them apart
Reported by the breadth pass; each item needs checking against its source before it becomes normative.
- Electrical conductivity - Exact reciprocal for linear isotropic media (σ = 1/ρ); same specimen, inverted unit S/m versus Ω·m.
- Electrical resistance - Extensive circuit quantity R = ρℓ/A; two specimens of the same material can have different R but the same ρ.
- Sheet resistance - R□ = ρ/t for a uniform film; four-point-probe semiconductor data are often R□ in Ω/sq, not bulk ρ, until thickness is known.
- Electrical impedance - Includes reactance; |Z| equals resistance only in the DC or purely resistive limit, so AC 'resistivity' from |Z| is not DC ρ unless the phase is checked.
- Surface resistance (as opposed to surface resistivity) - Resistance between two defined electrodes on a surface; surface resistivity is that resistance scaled by electrode geometry (IEC 62631-3-2 / ASTM D257).
- Specific contact resistivity - An interface figure of merit (Ω·m²), not a bulk material ρ; separated by transmission-line or Kelvin contact structures rather than a four-point bulk probe.
- Thermal resistivity - Fourier analogue (K·m/W) for heat flow; same word 'resistivity' in cable ratings, distinguished by the transported quantity (heat versus charge).
- Which of these neighbouring kinds and how to tell them apart hold for the sense of electrical resistivity this model covers, and on what evidence? provenance
Sources
- IEC 60050-121 International Electrotechnical Vocabulary - Electromagnetism (resistivity, IEV 121-12-04) - Specialist definition, quantity name, symbol ρ and SI unit ohm-metre in the electrotechnical vocabulary.
- The International System of Units (SI Brochure) - Coherent derived unit ohm-metre for resistivity and the relation of the ohm to the SI.
- ASTM D257 Standard Test Methods for DC Resistance or Conductance of Insulating Materials - Laboratory distinction between volume and surface resistivity, electrode geometry and typical insulating ranges.
- IEEE Std 81 Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of a Grounding System - Field practice for soil/earth resistivity, Wenner and related arrays, and use in grounding design.
- ASTM G57 Standard Test Method for Field Measurement of Soil Resistivity Using the Wenner Four-Electrode Method - Soil-resistivity measurement as used in corrosion and buried-structure practice, including customary ohm-centimetre reporting.
- IEC 62631-3-1 Dielectric and resistive properties of solid insulating materials - Determination of resistive properties (DC methods) - Volume resistance and volume resistivity - Current IEC method replacing older IEC 60093 for volume resistivity of solid insulation.
- Electrical resistivity and conductivity - Order-of-magnitude ranges by material class, relation to conductivity, IACS copper reference and common confusions with resistance.
What the second pass must settle
- Does the registry intend this entry to include complex frequency-dependent resistivity, or should that interpretation be linked to a separate electrical-response model?
- Should nonlinear apparent resistivity and differential resistivity be owned here, and which conventions would distinguish them?
- Which authoritative methods and sources should govern geometry corrections, uncertainty and applicability for metals, semiconductors, insulators and heterogeneous materials?
- How should effective resistivity of composites, porous media and spatially varying materials be distinguished from constituent bulk resistivity?
- Which neighbouring registry entries already own conductivity, sheet resistance and contact resistivity, and what relationships should prevent duplicate coverage?