X-ray Diffractometer Specifications

1. X-ray tube and power

• Copper target as standard with K alpha at 1.5406 Angstrom, with cobalt, iron or chromium options

• Conventional power of 1.2 kilowatts or more, high resolution types at 1.6 kilowatts or more, microfocus types lower power but higher brightness

• Focal spot size and target material must be stated

• Water or air cooling chosen according to laboratory conditions

• Note: the target decides what can be measured, since iron and cobalt bearing samples fluoresce strongly under copper radiation

2. Goniometer

• Radius from 240 to 300 millimetres in theta theta or theta two theta geometry

• Two theta range of at least 3 to 150 degrees

• Angular reproducibility of 0.0001 degrees or better with accuracy within 0.01 degrees

• Whether sample stage and detector move together or independently must be stated

• Note: larger radius improves resolution but changes sensitivity and footprint, so match to sample type

3. Detectors

• One dimensional array or two dimensional area detectors

• Energy resolution and maximum count rate should be specified

• Zero background mode or filters to suppress fluorescence

• Note: detector performance decides trace phase detection more than tube power does

4. Angular accuracy and resolution

• Peak position accuracy and full width at half maximum must be measured values, not claims

• Resolution is normally calibrated with standards such as LaB6 or silicon

• Instrument broadening must be controlled, or crystallite size and microstrain results are distorted

• Note: measured width plus standard reference is the acceptance criterion worth writing into the contract

5. Sample stages and attachments

• Powder holders, bulk sample stages and grazing incidence stages as basics

• Optional high temperature stage up to 1600 degrees Celsius, cryogenic stage and in situ cells

• Sample spinner to reduce preferred orientation

• Six or nine position autosamplers for batch work

• Note: in situ attachments add most of the value and should be ordered with the instrument

6. Software and databases

• Phase identification needs a PDF card database such as ICDD with stated coverage and licence

• Quantitative analysis with Rietveld refinement, K value method or internal standard

• Crystallite size and microstrain via Scherrer and Williamson Hall methods

• Raw data export for independent re analysis

• Note: database licences and software modules are often priced separately, so the quote must list them

7. Detection limits and quantification

• Typical phase detection limits around 1 to 3 percent by mass, with longer scans for trace phases

• Quantitative phase accuracy generally 1 to 5 percent absolute

• Standardless quantification requires a stated algorithm and working range

• Note: detection limits depend strongly on scan time, so test conditions must accompany the figures

8. Radiation safety and installation: the key item

• X-ray diffractometers are radiation producing devices, requiring a safety licence and certified operators

• Door interlocks, warning lamps, dose monitoring and emergency stop are mandatory

• Room walls and doors must meet radiation shielding requirements

• Stabilised power, cooling water loop and temperature control within 1 degree Celsius

• Note: the licence is a prerequisite, and sites often discover it is missing after delivery

9. Where procurement goes wrong

• Judging by tube power alone while ignoring detector and optics, so trace phases remain undetectable

• Software modules and PDF databases excluded from the quote, with core functions charged later

• Ignoring licence and room construction lead time, leaving the instrument unable to pass acceptance