Crystal structures can change when materials are cooled to cryogenic temperatures. These structural phase transitions may be closely connected to a material’s magnetic, electronic, mechanical, or other physical properties. Identifying the transition temperature and understanding how the crystal structure evolves can therefore be important in studies of functional oxides, magnetostructural materials, superconducting materials, correlated-electron systems, and other materials with temperature-dependent behavior.
Powder X-ray diffraction, or XRD, provides a direct way to monitor crystallographic changes during cooling. A phase transition that changes crystal symmetry can alter the positions and profiles of selected diffraction reflections. In some cases, a single diffraction peak above the transition separates into multiple components below it. Detecting this peak splitting requires an experimental configuration that combines reliable cryogenic temperature control with sufficient diffraction quality to distinguish closely spaced reflections.
Low-temperature structural transitions can be difficult to resolve because the resulting changes in a diffraction pattern may be subtle. Peak shifts or splitting may occur over a narrow temperature interval, and the selected reflections must be measured with enough clarity to reveal their evolution. Measurements near the lowest accessible temperature are particularly demanding because the experimental system must maintain suitable temperature access while continuing to produce interpretable diffraction data.
This application note examines a laboratory configuration based on an Empyrean diffractometer and an Oxford PheniX closed-cycle helium cryostat. The system was used to collect temperature-dependent powder XRD data from 320 K down to 12 K. A 1Der detector provided energy discrimination, which is relevant when rare-earth-containing materials are measured using Cu radiation because fluorescence can otherwise contribute to the measured background.
TbVO4 and DyVO4 were selected as representative materials with structural transitions at different cryogenic temperatures. TbVO4 undergoes a transition at approximately 33 K. Above this temperature, the selected reflection appears as a single diffraction peak. When the material is cooled below the transition, the peak separates into distinct components.
DyVO4 provides a more demanding example because its structural transition occurs at approximately 14 K. This is only 2 K above the lowest temperature used in the experiment. The temperature-dependent data nevertheless show a distinct change in the selected reflection, with peak splitting remaining visible close to the 12 K measurement limit.
Temperature-dependent isoline plots display diffraction intensity as a function of diffraction angle and temperature. This format makes it possible to see when a reflection begins to split and how the resulting components develop during cooling. The onset of splitting provides a direct visual indication of a change in crystallographic symmetry.
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Temperature-dependent X-ray diffraction measurements of TbVO4 and DyVO4 demonstrate the detection of structural phase transitions at approximately 33 K and 14 K, respectively. Using an Empyrean diffractometer equipped with an Oxford PheniX closed-cycle helium cryostat, diffraction patterns were collected at temperatures to 12 K.
The temperature-dependent data reveal the onset of diffraction-peak splitting associated with the structural transitions in both materials. The results demonstrate the ability of this laboratory configuration to resolve subtle crystallographic changes under cryogenic conditions, including a transition occurring only 2 K above the lowest temperature used in the experiment.
Many functional materials undergo crystallographic phase transitions when cooled to cryogenic temperatures. Characterizing these transitions can be essential for understanding relationships between crystal structure and physical properties.
Such measurements can be challenging because changes in crystal symmetry may produce only small shifts or splitting of diffraction peaks. The experimental configuration must therefore provide both access to the required temperature range and sufficient diffraction quality to distinguish closely spaced reflections.
This application note demonstrates low-temperature XRD measurements using an Empyrean diffractometer equipped with an Oxford PheniX closed-cycle helium cryostat. TbVO4 and DyVO4 were selected as representative materials because their structural transitions occur at approximately 33 K and 14 K, respectively.
Powder X-ray diffraction patterns were collected while the samples were cooled through their respective structural transition temperatures. Selected diffraction regions were evaluated as a function of temperature to monitor changes in peak position and profile.
Temperature-dependent isoline plots were used to display diffraction intensity as a function of both diffraction angle and temperature. In these plots, the onset of peak splitting provides a direct visual indication of a change in crystallographic symmetry.
The 1Der detector was used for the measurements. Its energy-discrimination capability is particularly relevant when measuring rare-earth-containing materials with Cu radiation, where fluorescence may otherwise contribute to the measured background.
| Parameter | Measurement condition |
|---|---|
| Diffractometer | Empyrean |
| Sample environment | Oxford PheniX closed-cycle helium cryostat |
| Temperature range | 320 K to 12 K |
| X-ray radiation | Cu Kα radiation, λ = 1.5406 Å |
| Incident-beam optics | iCore for Cu radiation |
| Diffracted-beam optics | Fixed anti-scatter slits medium |
| Detector | 1Der detector |
| Sample form and mounting | Powder sample mounted using grease |
| TbVO4 temperature sequence | 55-90 K in 5 K increments; 12-55 K in 1 K increments |
| DyVO4 temperature sequence | 0.5 K increments across the selected transition region |
| Scan range | 10-90° 2θ |
| Step size | 0.0167° |
| Measurement time | 20 minutes per scan |
![[AN261006-figure1.png] AN261006-figure1.png](https://dam.malvernpanalytical.com/9cc3233c-773d-40b7-8060-b4da00713d1a/AN261006-figure1_Original%20file.png)
TbVO4 undergoes a structural phase transition at approximately 33 K. This transition changes the crystallographic symmetry and produces splitting of selected diffraction reflections.
At temperatures above the transition, the selected reflection is observed as a single diffraction peak. As the sample is cooled below approximately 33 K, the peak separates into distinct components. The onset and subsequent development of the splitting are clearly visible in the temperature-dependent isoline plot.
The measurement demonstrates that the Empyrean and PheniX configuration provides the temperature control and diffraction quality required to follow the peak-profile changes associated with this cryogenic structural transition.
![[AN261006-figure2.png] AN261006-figure2.png](https://dam.malvernpanalytical.com/18503d13-734a-47ce-83ec-b4da00713c08/AN261006-figure2_Original%20file.png)
DyVO4 presents a more demanding low-temperature measurement because its structural phase transition occurs at approximately 14 K, only 2 K above the lowest temperature used in the experiment.
The temperature-dependent diffraction data show a distinct change in the selected reflection near 14 K. Peak splitting remains visible in the isoline plot, enabling the transition to be identified despite its proximity to the 12 K measurement limit.
This result demonstrates that interpretable diffraction data can be obtained close to the lowest temperature reached with the configuration. The measurement is therefore relevant to applications requiring both cryogenic temperature access and sensitivity to relatively small changes in diffraction-peak profiles.
![[AN261006-figure3.png] AN261006-figure3.png](https://dam.malvernpanalytical.com/c1b37b10-73da-4e03-9ae6-b4da00713ab9/AN261006-figure3_Original%20file.png)
The measurements demonstrate four capabilities relevant to low-temperature materials research:
The Oxford PheniX cryostat enabled temperature-dependent XRD measurements from 320 K down to 12 K, providing access to structural changes occurring far below ambient temperature.
Peak splitting associated with the structural transitions was observed in both TbVO4 and DyVO4. This allows the onset and evolution of each transition to be followed directly from the diffraction data.
The structural change in DyVO4 was resolved at approximately 14 K, only 2 K above the lowest temperature reached during the experiment.
Temperature-dependent isoline plots provide an accessible way to identify the onset of a structural transition and examine how selected diffraction features evolve during cooling.
The Empyrean and PheniX configuration is relevant to temperature-dependent XRD investigations in which structural changes must be followed under cryogenic conditions. Potential areas of research include:
The suitability of a particular configuration will depend on the sample, reflections of interest, required angular resolution, temperature sequence, and measurement-time requirements.
Temperature-dependent measurements of TbVO4 and DyVO4 demonstrate the use of an Empyrean diffractometer equipped with an Oxford PheniX closed-cycle helium cryostat for investigating structural phase transitions at cryogenic temperatures.
For TbVO4, the onset of diffraction-peak splitting was observed below approximately 33 K. For DyVO4, the structural transition was resolved at approximately 14 K, only 2 K above the lowest temperature used in the experiment.
The results show that the configuration combines cryogenic temperature access down to 12 K with the diffraction quality required to observe subtle peak-profile changes. Temperature-dependent isoline plots provide a direct visualization of the structural evolution of both materials as they are cooled through their respective transitions.
The Empyrean and PheniX configuration therefore provides a practical laboratory approach for investigating materials whose crystal structures evolve at cryogenic temperatures.
| Measurement | Result |
|---|---|
| Instrument configuration | Empyrean with Oxford PheniX closed-cycle helium cryostat |
| Measurement temperature range | 320 K to 12 K |
| TbVO4 transition | Peak splitting observed below approximately 33 K |
| DyVO4 transition | Diffraction change resolved at approximately 14 K |
| Principal observation | Temperature-dependent splitting of selected diffraction peaks |
| Scientific value | Direct visualization of structural changes under cryogenic conditions |